1. Audio Plays/Dramas
Paizo and Big Finish have done an awesome job with their Audio Dramas of the "Rise of the Rune Lords" adventure path. However, as I have said in my reviews (here and here) they could have been better. I think WotC has the ability to do that with its amazingly large and varied settings and adventures from nearly 40 years in the business. I think the best route for them would be through Graphic Audio.
Graphic Audio's Tag Line is "A Movie for the Mind" and it truly is. The narration, vocal cast, music, and sound effects are top notch and I think they would bring a lot of awesome to the D&D brand.
2. An official Meta-movie
I have often said that "The Gamers: Dorkness Rising" is the best Dungeons and Dragons movie ever made. Why? Because it focused not just on the story of the fantasy world but on the players and the drama of the table. The best part was that it was done with respect and love (unlike some other recent examples). A big budget action comedy from the same cloth as Dorkness Rising would be amazing.
3. A Return of a Modern Source Book
5e doesn't need as much work to build a modern setting with as 3.5 did and while there is a plethora of modern settings now available (hell I'm working on one). D20 Modern will always be a favorite in my heart. I would like to see some support from WotC for this coming up ... and I mean more than the rare article on their website.
4. A return of the Cartoon
The original cartoon had a lot of fun elements involved but was somewhat hampered by a horrible budget, no real support from TSR and 80s parents groups. Thankfully almost all these problems are easily taken care of at this point. Hasbro is the parent company of Dungeons & Dragons and can both give an animated series a deserving budget and support it through Hasbro Studios (the toy and game company's media arm). The only thing missing is a writing staff that knows D&D and at this point I pretty sure they could throw a stone at the Writer's Guild and find 20.
5. Better Digital Support
This is something that will be showing up in my next youtube video and is something I feel ALL rpg publishers who also release on VTTs should do but would love to see WotC become the forerunner of it. Basically if I paid full price for the physical product why should I then have to pay full price for the VTT version. Marvel Comics does this wonderful thing (or did. I haven't bought comics in a few years) where if you bought the physical copy you'd get a code for the digital copy. I understand the work that goes into converting adventures from paper to VTT - as I am currently doing it for my own adventures - however, at least a 25% discount should be in order to people who have legally purchased the physical copy.
BONUS ROUND: A Blasted OGL!
I really don't have to explain that one.