All of your efforts should point the north of fixing the well known "feet in the mud" problem, because it is indeed horrible and makes alot of people throw up and forget about Vavoom before they consider learning to juice out any of it's features. Honestly, I was tempted to do so but dropped the idea for the sake of my own map which wouldn't be possible without slopes and 3dfloors.
I hate models, I prefer oldschool sprites and I want them to be fully visible, feet matters for me!.
Another request would be a proper decal system and faster mouse movements, but again, nothing beats the relevance of a possible fix for the atrocity pointed above, if you can do that, I and many many people will be set, trust me, Vavoom is great and would gain the fame and status it deserves if it could render the whole sprites as any half-assed Doom port from late 90's.
Regards.