I'm still on the fence. I agree that if they could draw in new blood and even a fraction of the lapsed AD&D players...it would outsell 3e, 4e, and maybe PF sales combined...
BUT....
How in heck would they pull that off.
Thus far, 5e actually does NOT bear enough similarities to older AD&D or D&D to really draw them in for the lapsed players, so you'd have to try a campaign where you fool them into buying (which as we saw with the 4e Starter/Basic redbox set...doesn't work as well as intentioned at times, these guys are smarter then you guys think).
In addition, you're trying to ply on their nostalgia...which while powerful...can also be a hard thing to wake (sure, we have the guys that saw GI JOE and Transformers movies due to their youth...but then you also have flops based off franchises from the past as well).
Which leave new blood...that may or may not work. We'll see what they come up for an advertising campaign.
As it stands now, I think we'll have a surge of people buy the core books, mainly the players now, and some PF players and maybe a few hobbyists. Sales will initially be strong...but after the core I think the old school and PF folks will stick with their games for the most part. I think we'll see more of the old school folks actually play 5e with most of PF being a loss at this point. The 3e players that did not switch to PF, I think we'll get a good chunk of those, and probably 50 - 60% of the current 4e players.
Anything past that will probably depend on the advertising campaign...and much of that will be in regards to new blood. This is a delicate balance. I'd push for a TV and internet search engine/tube campaign in the range of up to tens of millions perhaps...but that is a MASSIVE gamble. You're spending just as much if not more than you expect in the initial sales at this point to try to advertise in that way...which means if you DON'T get the massive new blood input, you've just spent an ad campaign that will sink your product in and of itself alone (in otherwords, the cost of advertising is so much, that even without any other factors, it causes a negative on the product profits).
On the otherhand, a successful one could revitalize D&D. My guess is they will vote against the TV and massive campaign...and go with the softer campaigns to an installed base...in which case I think the sales will follow very similar lines to what I outlined above in regards to core sales and who will stick with it after that.
That's not a great sales line to follow though...and unless we have hardcore followers that buy everything (not really happened with most products in D&D, though I think 3e FR folks may have been the closest to that), I'm thinking this is not a great foreboding for the product line.
However, we'll wait and see what the current managers of the brand come up with in promotions and the end sales results I suppose in regards to D&D next as it's still a while to go and nothing's been written yet.