Elder Scrolls VI: Equestria.
Seriously though I would love to see what Elder Scrolls is like with those resources.
The other ideas are of course the obligatory Pokemon MMO: 3D active combat where you control each pokemon third person.
Then when it is the best Pokemon game ever it will replace the game boy ish series and new pokemon will be released in expansions and random patches for people to discover on their own.
The Pokedex will record the character name of the first person to catch one.
Those are the only games I could justify that level of development cost on.
Games that won't ever end.
I'd look into the JRPG or Dragon Age esq angle as well but I don't think they support as high a resource cap as something like Elder Scrolls.
Could you fathom Elder Scroll X: Nirn!?
Rather than focusing on a region of the continent Tamriel, it is literally the entire world.
Of course many of the planes of Oblivion and other dimensions would appear.
There would be a greater inter-dimensional threat that makes up the final boss of the main story with 5 forms at least one of which is 27 stories tall.
We'd have mounts, pets, companions, flight, mounted combat, flight combat, mounted flight combat, underwater cities, space cities, magic capable of replicating the Portal Gun, shrinking magic, tiny people houses hidden throughout all of the word where only people that can shrink can explore the areas and quests.
We'd have all of those filler items have a purpose, built in art tools for paint and canvas to decorate your house.
Custom clothing editors a-la APB.
Some system to renovate houses that you own, or entire kingdoms you conquer.
A lot of resources would be put into locational damage and tangible models so that wolves don't look like they are cast out of rubber when they die.
I'd take a page from Jean D'Arc, where if a dragon occupies 9 squares then a 9 square AoE hits 9 times because of the surface area.
I don't even know, name it and it could happen.