With the announcement of the 5th Edition of Dungeons and Dragons, Wizards of the Coast is making an active effort to attract all D&D fans to the same edition. I fully expect they will try to do just that. But there will inevitably be choices that have to be made where the philosophies underlying 3e and 4e are different enough that they will have to choose a direction. When confronted with that decision, going in favor of the 3e fans will be the smartest move because of two things: GSL and OGL.
Let me say at the outset that I am not saying Wizards should or should not do this, I am only predicting that they will. I am not a fan of 4e, but I also do not take it as a personal affront. I would like to be drawn back in to D&D with the release of 5e, but if I am not there are plenty of games for me to play. As pen and paper gamers what we have in common outweighs our differences, and if others like 5e and I do not, that is fine.
When 4e was released, Wizards faced a huge problem in that OGL allowed other companies to continue to actively develop 3e materials, and to develop a wide range of materials derived from the 3e rules. I believe Wizards recognized that mistake and rectified it with GSL. I do not mean it was a mistake from the perspective of the health of the industry as a whole, just from the point of view of Wizards trying to draw people to a new edition. For those who did not like 4, there were actively developed, quality 3e products being produced by third parties. OGL material has been so successful that Wizards is making a concerted effort to draw in the not insubstantial portion of the player base that stuck with 3e.
GSL is a different story. Wizards can terminate GSL. Entirely. They can get rid of it and stop third party publishers from using GSL. The termination provisions of GSL that are instructive in this regard:
"10.1 Termination. Wizards may terminate this license and the rights granted hereunder automatically upon written notice to Licensee or upon posting on its web site a termination of the GSL as applied to all licensees."
Section 10.3 spells out just what happens when the GSL is terminated. The FAQs that go with the GSL make it clear that if Wizards issues a wholesale termination of GSL, third-parties operating under the GSL have six months to sell off their inventory and then they are done.
So how does this impact design decisions?
If Wizards truly wants to bring both 3e and 4e players into the fold with 5e, it makes sense to go after the 3e players. Those are the players who have quality, ongoing, actively-developed materials keeping them happy. If GSL is terminated, 4e players have nowhere to go. Sure, they can continue to use their 4e materials indefinitely - no one disputes that. But for many there is an allure to an actively developed game. For the 4e players, the choice will be to go with 5e, move back to OGL-related games (in which case a Wizards decision to move in that direction is another win), or move to other game systems entirely.
If Wizards makes design decisions in favor of 4e, at the expense of the 3e community, the 3e players have plenty of options. They will stay right where they are now, and it is clear Wizards is not happy with that situation.
What I have said above does not apply to every design decision. The goal of 5e is to be modular, and to cater to a wide variety of play styles and preferences. To the extent they can do that, I believe they will. But when it comes to those areas where they have to make a choice, where they have to swing in favor of one or the other because at some base level things are just too incompatible, they will move toward attracting the 3e players. It is the only move that makes sense.