This probably has been questioned before, but since I admit not being a regular here (although I scan the Mods forum daily), I just can't resist my curiosity:
Why did Bethesda cease to work on Oblivion? There's so much room for large and small expansions. The engine remains very powerful and many technical updates were made possible through the release of both Fallout games. This is a very strange marketing/development decision.
Having some experience in this industry, I'm aware that maintaining a content development team is costly, and the resources required to put together a fully fledged expansion like Shivering Isles does not easily come by. However, take Valve for instance. They are known for keeping an eye on player created content and integrating them with their Intelectual Property. They managed to turn Counter Strike, for instance, into a highly lucrative business. Mods like Deadly Reflex, MMM, and Oscuro, to name a few, have had over a million downloads and continue to expand. If you were to fully integrate them into Oblivion, in a, let's say, Ultimate Oblivion release, and charge only $10 for it, there's over U$10.000.000 in raw profits for very little actual development. Possibly much more with the media coverage. Look at how many bugs UOP managed to squeeze, that's hours and hours of development free of charge.
I'm not implying you should blatantly "steal" people's work and turn them into company cash...but I'm willing to bet many in the community would be more than happy to be acknowledged by having their pet projects become part of Oblivion, not to mention most would love to see Oblivion expanded and continued in some fashion.
Behold amount of landmass that could be expanded in every direction with a very small team of worldbuilders. People would happily pay for those! If there's a huge concern about the expenses of maintaining a team of modellers and scripters, why don't you buy those assets? It'd be far more cheap, seeing there are tons of people already working on them for absolutely nothing in return! If you were to support PC only DLCs, look at the amount of eyecandy and graphical features that could be added to Vanilla Oblivion, bringing it closer to the designers' original vision. You have, after years, a massive community, which is very impressive for a single player game. Why isn't anybody taking advantage of this, but the players themselves? It feels like someone's sloppy decision to sit back and relax and let others finish the business.
You have an engine capable to be deliver powerful graphics, even by today standards, but with some limitations that were a major issue years ago. But today, with more powerful machines and forgiving deadlines, there's room to expand and to polish leftovers from the initial release. You could even work together with those responsible for enhancing the scripting capabilities of Oblivion by incrementing the amount of tools available for the community. The potential is limitless, and you'd be ensuring the community could last for many more years, while still bringing in resources to fund other projects, ES5 included.
And yet, the official DLCs available are so minimalistic in scope, and clearly a discontinued project. Can't any of the CEOs see the amount of potential profit being wasted here? And it's not like the engine is getting any younger...Heck, if this was my company all the other provinces would probably be fully explorable by ship, perhaps with fully configurable dynamic shadowing and an intelligent companion system toggled by a radial menu.
All in all, I really think Bethesda should take a hint from the amount of content people have been voluntarily creating just because they are passionate about the game. Give your own game some love!