Alot of manufacture are sending OTA updates to phones enabling 720p vid recording. So I think its not that impossible, I think the hardware is capable, but needs hacking-coding-etc to make it work.
There's someone on youtube who claims to have been able to modify the hardware of the N900 to capture 1080p video. The poster is German, and I failed at using a translator, so anyone want to give it a try and ask the poster how he/she did it?