After his transformation, will the blight continue his experiments on the other killers or will somone else find his notes and pursue the florid nightmare.
Any future blighted cosmetics can simply be explained away as being before Talbot's transformation. Time is not linear in the Entity's realm.
He's too unstable to continue his experiments and no other Survivor that we see knows how to deal with the Killers like he did.
So if time isn't a line and more of Jeremy bearimy then Talbot would know the existence of other killers outside the killers we already know exists
The best example of this would probably be Plague. Historically, she would be the oldest Killer, but for all we know, she could have been the most recent arrival when Talbot began his experiments.
Theoretically, this could also explain why none of the licensed Killers have blighted cosmetics: they came into the realm after the experiments were already done.
Pretty sure that the Blight is still experimenting with Survivors from the info of some of his add-ons and we know that Killers can meet each other in the realm, so the Blight would have a lot of chances to create more “blight” versions of killers.
Maybe on Survivors, or those add-ons are from before his transformation. The Hunger tells us "He'd rip survivors and killers apart limb from limb for that feeling again." This was before he transformed. During his time as a "Survivor," I don't get the feeling he was entirely... friendly. Given his state of mind when he entered the realm (carving Death is only the beginning into the stone until his fingers bled and then into his chest), I don't think he was interested in really helping the others, and we also know Survivors can kill each other, through Arcus 893, which says "The other Survivors drowned him in mud to shut him up." Death is heavily implied.
And the thing about Killers meeting each other in the realms directly conflicts with other statements made that they are in their own realms until pulled for trials, with the Legion being the only ones who are able to meet each other.
Talbot wants the serum for himself, and only himself, now as well, only occasionally using it to murder Survivors. Even if he is sane enough to experiment on other Killers, and even if he CAN reach those other Killers, his addiction could be too powerful for him to overcome now.
But it is not confirmed that Talbolt meet with survivors at all during the time where he was experimenting with Killers and more importantly, the description of the add-ons mentions that is from a recent survivor,not something from the past:
A chemical squeezed from the pineal gland of a recently deceased Survivor.
His mori for me seems to be experimenting with the serum on survivors, yes, he is addicted now, but the desire to experiment, to research and to know is still there, and even in the Void, he still wanted to use the serum to know more about the realm, which is probably the only thing left of Talbot now.
He feels the hunger. Not for food or drink. Not for talk or fun. For a flower. A single flower. For serum. He knows The Entity is watching him. He knows it. Feels it inside his bones. He doesn't want to be snatched for another trial. To suffer or cause suffering. And to what end? The great horrible mystery of it all. He wants to understand this place. He does. But he senses that to know… to really know would drive him… mad. Madness. That's what this place is. The embodiment of madness. He doesn't want to be pulled into another trial. He wants to return home. He must return home. That's why he was studying the serum. It gave him insight. Insight to what? He doesn't remember.
Although we know that there is enough of him to remember portions of his past with some of his add-ons, so he is not some insane beast:
A poisonous plant that sparked Talbot's interest in chemistry. It rekindles deeply buried memories.
A ring given to chemists graduating from the London School of Medicine. It's a reminder of unrestrained ambition.
Talbot's traditional experimenting days are probably now past him since he promises to rip both killers and survivors apart if the Entity provides more serum in the Hunger. Still, as others have mentioned, his usage of serum in the mori and his addons suggest that he still harbors the scientific and curious tendencies that got him where he was to begin with. Plus, time is jank as hell, so we'll keep getting Blighted cosmetics because they look sick and because it can be summed up as Talbot experimented on X killer before he became the Blight.
That the part after he got addicted from the rat accident and the flowers died and he couldn't find anymore. The Entity took advantage of that and turned him into what he is now. Dude is driven crazy by the Entity.
He experiment on a dead rat with the serum. The rat come back to life for a short time and bite him, which made him addicted to the serum and made him very powerful. He only experimented on the killers when he was a survivor.
Talbot wanted to help people with his potions. He didn't know his potions caused deaths, when he learned about it he felt guilty and wanted to redeem himself.
(carving Death is only the beginning into the stone until his fingers bled and then into his chest)
His research were taken from him by the 'School' that saved him and he was trying to get it back. He wrote that later because the Entity started whispering to him and he wrote what he thought was his research on the walls of the room with a stone. After that the Entity took him and forced him to join the trials like the other survivors.
After his transformation he will harm both sides equally. You can thanks the Entity for that.
It will be kinda funny if Talbot is still trying to get out of the Entity realm with each Hallowed Blight. Giving the Entity a royal headache about it.
The Blight's lore and existence as one of the Killers are proof he won't be able to really continue towards his goal.
Killers are all bound to serve the Entity. Some, like Pyramid Head, are in a strange sort of alliance with it, while others, like Trapper, have been so warped and tortured into servitude that almost nothing of them remains (it's an outdated idea now, but the original lore of the Killers characterized them as inhuman beasts rather than people).
Talbot is no exception. The climax of The Hunger story in his lore was how he failed to overcome his addiction and the powerful pull of the Entity. He could have been another Vigo, but he failed and was twisted into the Blight.
It's possible that some part of his reasoning mind is still inside the monstrous creature he turned himself into and it's possible he still performs experiments. But it's irrelevant now.
He belongs to the Entity; the goal of his research (to be able to use the Serum to traverse the Entity's Realm freely and unhindered like Vigo can/could) can no longer be achieved.
It's possible some other lore character might learn from his mistakes, but for Talbot Grimes it's over.
They can make him another Vigo even after his transformation. His main goal from making the serum is to get out of the realm. During the Hallowed Blight the Entity become weak and he have this knowledge about it. He already know how to make the serum from the flowers and can keep experimenting to get out with each Hallowed Blight, I mean he was able to get out of the void already. He should be more in control during this event instead of the Entity because of this. They really can do many interesting things with him and hope this is not the end of his lore.
What if his too interested to leave the realm?
*for some reason my comment disappeared each time I post it*
He got addicted to the serum by accident. The reason for all his experiments is to get out of the realm. He was able to keep himself out of trials after the experiments and was able to go through different areas in the Entity's realm where no survivor or killer can go. He still has this ability for sure.
Devs mentioned in their latest video that the idea for Talbot is Jekyll and Hyde. This could mean Talbot (Jekyll) is still in there fighting to break free from Blight (Hyde) and he is not completely driven crazy by the Entity. It would be interesting if Talbot was able to free himself because they established with Felix's father, Janos, that the Entity can be fought.
Talbot is one of the few characters that impacted the story and it will be a waste if they decide "yeah he is a killer now, that's about it".
Y'know what'd be funny? if the other killers would put together and put a bounty on Blight's head, enlisting Deathslinger's services (he's have to make himself immune to the serum first, but I think he could)