My biggest concern about the future of the D&D game is this.
3e was designed by people who cared a lot, and who had enough of the traditional "old school" thought. Monte Cook worked on 2e products, Skip Williams was there from 1e, and Jonathan Tweet was the new "young turk". Together, they revamped a system but kept a lot of the old flavor in. And at that time, Wizards had just purchased TSR and there was still a TSR culture.
But as the game has progressed, it's changed thanks to the influence of WoTC R&D, etc. While this isn't a bad thing per se, you'll note that the rules took into account more miniatures, squares for instance, and there are elements I see that are designed to remove the dependency on the DM. When 3e first game out, I was glad they made people feel less "guilty" about "min-maxing" or power gaming. All styles of play are valid. But it seems that there is no longer as much emphasis on the story or background.
And note the loss of the "TSR" culture. What big names are left at the company? Most formed their own d20 labels which have suffered a lot--or completely retired or moved on to CRPGs. I think Monte had the best success but now he's retiring. I feel there's a loss of direction there and there's no one to keep some of the magic that made D&D DUNGEONS AND DRAGONS.
What I think might happen:
4e comes out as expected. Emphasis is on combat and minitures, the DM's role is reduced. Things like death, etc, are reduced in a way similar to Mike Mearls columns. This may happen in 2008. The game will not be OGL, no SRD will be produced. It will still be compatible but the company will emphasize minis because that's a lot harder to copy and post on the Internet.
The game gets short term new fans. Older fans dislike the changes.
The game has a disapora of players who follow various systems. Sadly, because of the OGL, this may allow the game to survive, but it will become factionalized. Some publishers will attempt to do a 3e compatible OGL game, but the competition and lack of Wizard's industry power will likely prevent any one from coming too powerful.
RPGs might not be spun-off--at best I could see somebody spinning off a Forgotten Realms RPG project or sell the Novel division.
Hasbro will NEVER give up the D&D Trademark.