The more I mull this over, the more I think that, aside from any issues of whether they can actually pull off their goal to make an edition that appeals to everyone (which I think is utterly quixotic) WotC is going to have to overcome the inertia of whatever players are already playing.
In 2000, 2e was a spent force and people were looking for something new. 3e was similar enough to keep people invested in the brand while different enough to freshen it up. This helped to overcome the inertia of the current system and a lot of people made the switchover.
But WotC keeps going back to that well and they find themselves increasingly unable to overcome the inertia of the current system. So, players put up with the changes from 3.0 to 3.5 because they see it as basically the same system (even though the revisions were too substantial to make it easy to meld 3.0 and 3.5 as they had originally promised, and even though it came out relatively soon after 3.0).
For players like me, 4e was too soon again after 3.5 and too different from the preceding systems to overcome the inertia. I would have kept playing 3.x even if Pathfinder hadn't emerged on the scene. What Pathfinder did was enable me to better maintain my inertia by giving me new material and very high quality stuff to spend my money on. The failure to overcome the inertia of a substantial portion of the fan base was a fatal flaw in the transition from 3e to 4e.
And now we're transitioning again, and too soon for many players of either of the other editions. When a current edition is maintaining its vitality (like both 3e and 4e and unlike the last days of 2e), then even if it's not making its profit margin, its very difficult to make the case for a new edition, since, as many people have noted, it will fragment the player base. The issue is not only timeframe but how invested players still are in their preferred edition.
So it's highly likely that 5e, whatever it attempts to do, will fail to overcome the inertia of either the 3e or 4e communities. Add in those committed to the retro-clones and their own inertia and WotC has painted itself into a massive corner.
As a 3e player, I feel like I'm in a better position to maintain my inertia than the 4e community might be because of the OGL and Pathfinder. The limitations on the 4e licence will make it harder for 4e players to continue to maintain their inertia after the game goes out of print (though many will undoubtedly do so).
So regardless of Monte's involvement, I'm going to be very intrigued to discover if WotC is able to produce something that can accomplish its design goals, satisfy players of current systems, and ultimately overcome the inertia of the current system for enough players to make it worthwhile to put aside their current investments in characters, products, and stories to try something new.