Better battery life
smooth transitions
deleted non needed games and replaced with emulators or emulators like picodrive with few games
installed simple cleaner for trashy files folders like clean900
newer BROWSER the BIG deal!
maybe facebook app or smth like that
replace original cam with rich features like manual focus for taking pictures and filming
more codecs like filming on 720p and for playback
hotswamp???????
full phone control on hw keyboard
non lagy phone portrait rotation
manual phone vibration control
no video on boot or change to short clip without sound
make all swappolube configs in n900 without the app
install lowmemmode
remake settings app from scratch without that laggy scrolling
replace original media player with openmediaplayer or other app to be fast with equalizer and fully controlable with hw keyboard
make power-kernel as default
replace original photo viewer with solid pictures editor non laggy scroll and fullcreen picture view
let us watch videos in fullcreen without those striplines on top and bottom
maybe develop new app to easy download newest firmware and fast flashing the phone without cmds xterms just with green light that shows everything is ready just press flash and wait! its 2014 and we still use the old principe for flashing that black phone god!

i think if all of those settings will be in next cssu nokia will suck balls and starts to get back our beloved n900s cheers from Lithuania!!