I don't think they'll be making a "quick" adventure game, RTS, MMORPG or anything like that as it may soil TES good name as durable games.
A http://www.youtube.com/watch?v=HCAu814nh84, would fit right into the world.
Basically, you could sail around Tamriel; smuggle goods, recruit crew and train them, buy new ships and upgrade them...
As for the rest it would be basically a regular TES sandbox, with a main-quest, Deadra, factions and all that good stuff.
The main difference would be the map system. Basically you would have one world map of Tamriel, where you can go to and explore, say 100 different locations ranging from harbors to pirate-dens, deserted islands, etc...
I think it would work as a spin-off, or stand-alone series set in the same world.
Also it would be great to throw a new light on the franchise, would be great experience/exercise for both the fans and developers.
They shouldn't be afraid to do something different, as Oblivion, FO3, Skyrim is all basically Morrowind in a new coat.
But nothing "too" different that will start as a great idea and then end up svcking, like most of Molyneux games.