Crossbows. Considering assets for them already exist in Update.bsa from 1.5.
Personally, I'm hoping to see that seasonal weather stuff next. That would be the absolute best thing I could ask for now that the navmesh bug is fixed.
Hmm... they need to offer much more for magic than they currently do. I'll take that before seasonal weather, especially since Realistic Lighting, Better Snow, and Natural Rain already bring weather to life quite nicely.

Combo spells, but really just having far better staff availability would be fine... and offer wands if you are going to do anything with weapons, Bethesda, long before worrying about spears, crossbows, or any other typical physical weaponry!

(okay... I'm calm now... really...

)