I don't know if I necessarily agree. Even though Oblivion was obviously made to appeal to a larger and more casual base, it's still one of the most complex, innovative, and truly immersive experiences one can experience in a game. I definitely enjoyed Morrowind than I did Oblivion, but you also have to keep things in context with the development of Oblivion. Bethesda had started work in 2002 immediately after Morrowind. They were making Oblivion for a generation of console that didn't exist yet. That meant they more or less had to guess for 3 years how the game would work on next generation technology, and what they actually wanted to do with it. Bethesda only had 6 months to actually work with the hardware when they finally got it, so I can understand why the game wasn't as well made as Morrowind. With that understood, I really do hope the lore, content, size, and immersion is brought back to at least the extent that Morrowind had. I like to believe that Bethesda is one of the best RPG developers in the industry today. With that understood, I believe they are more than capable of making a game that appeals not only to the new/mainstream player base for TES, but also their old school fans.
You make some good points - and deepness of lore is probably something they won't skimp on.
Still, there are some complexities that we will never see. Fire up Daggerfall and check out character creation - all the intricacy of the insane amount of skills, strengths and weaknesses. You practically need a guide just to get out of the first dungeon.
There are a ton of things that overlap - things that both a broader audience and the old school RPG crowd can enjoy - but there are some things that can't, and that's a game breaker for most people. WOuld TES V sell as well as Oblivion or Fallout 3 if it had morrowind style combat (to-hit determined by dice-rolls)? Probably not, but I'll be the first to admit I'd prefer that system over Oblivions.