4e... My thoughts.
Rules:
I think there are plenty of clever ways the core rules could be streamlined and simplified in areas but it really does need to break some new ground in order to make it distinct from 3e. How? Topic for a different discussion… And I definitely agree the brand the name (Dungeons and Dragons) should not be diluted by a myriad of variations on it.
Do not ignore the digital revolution –
be the guiding hand in it. Build a lush online gaming experience for your players. Allow them to buy digital versions of adventures that you can run in virtual tabletop games (chat and message board style). Offer a free service with X amount of functionality and a pay for service that offers all the goodies and eye-candy for your online games.
Miniatures:
Here’s where I would focus no small amount of attention. While the game would not require miniatures, the idea is to make them so attractive (especially to newcomers) that you wouldn’t want to play the game without them. The first order of business - increase the grid scale from 1” to 1.5” and increase the size of the miniatures appropriately. The new 4e line of larger miniatures would fall under two banners…
1.
The “Baseline” Miniatures Line: Pre-painted, well-made and affordable. Their larger than normal size will allow for better detail than their smaller cousins, making them more attractive on the new tilesets/battlemaps.
2.
The “Masters” Miniatures Line: As you might guess - a high quality line that is a clear cut above in detail, color… and naturally, price. For humanoid figures there would be limited pose-ability with hands and arms free for “accessories”. One of the biggest drawbacks to standard miniatures has always been finding one that matches your character. With the Masters Line, you could buy box sets of accessories to gear up your mini (weapons, shields, magic items, legendary artifacts…) to have at least some customizability. McFarlane toys to produce?
Masters Line monsters come with their own “Monster Card” with a picture of the beast on one side and the relevant stats on the back. Appropriate monsters come with a variety of gear. Giants for example could come with a “boulder”, a sword and a club.
D&D – The Animated Series:
Time to build those marketable icons.

Forget about movies, at least to start. Animated is the way to go. The title of the show should focus on a brand you want to create under the D&D banner (eg. Greyhawk, etc. or something entirely new), rather than D&D itself. You do want to associate it with D&D but at the same time you want to distance yourself from it a little at the same time.
The series should be “semi-dark” in nature (but not too grim for the young teens) but mature enough that adults will enjoy it too (complex relationships and personalities). That is, a little more mature than the JLU, but not animated Spawn dark. After you gain some momentum, tie in with the merchandising… minis, books, comics, larger scale action figures, board games and supplements to the RPG proper.