all of tamriel, with more landmass than great Britain- we could even go bigger than that ( http://www.youtube.com/watch?v=SeoT_cz2nC0 )
every city as large as city's were depicted in assassins creed.
tesselation, awesome textures and perfect animation
a REAL particle system (dynamic smoke, and maybe water)
lifelike ai
but most of all-
we could have some kind of epic plot concerning all of tamriel. the empire has failed right? what if we could build each nations trust, form alliances, wage war, form strategys, betray entire nations. raise citys?
for starters- the player could unite the dumner people (who are refugees due to morrowind being invaded). then unite the nords. then get the nords and dumner to attack morrowind and combine morrowind with skyrim with both nords and dumner being equal in everything. a counter attack from argonia may be likely, so the player may choose to be an ambasodor/general of either the dumnords, the argonains provided nobody knows who the player is, or even do something else entireley like getting elsywere to attack argonia .
the player could try to go for anarchy- they could break up the bonds between valenwood and summerset and put those in a civil war, while getting hammerfell to attack both countrys. then the player go necromancer on their asses and attack all 3 parties with an army of undead. maybe even start a war with another necromancer such as the king of worms (i refuse to believe the mages guild questline in oblivion is canon)
after this the player could help the dumnords reclaim the war ravaged land easily. (high rock is only small, so a diplomatic relation should be easy) and set up a new empire.
of course- the game will remain a first person rpg of immense detail :intergalactic:
with more detail than daggerfall,skyrim and morrowind put together