Just for flavor, I think it would be neat if Demo transitioned to running on all 4 limbs when in bloodlust 3 (killer camera would lower to Hag level as a result).
It would look cool, but it would disadvantage the killer in a couple of ways. Firstly, it's harder to see the survivors behind objects and such when you're shorter, which (killer mains correct me if I'm wrong) would make it more difficult to stay in the chase and keep Bloodlust up. and secondly, it would make it super obvious that the killer has BL3. Right now, only experienced survivors who pay attention tend to notice things like that, but giving the survivors a clear visual cue would put low ranked killers in particular at a disadvantage.
Not sure it would be worth adding special stuff for a band-aid mechanic that only really exists because of bad map design.