In one corner we have Wizards of the Coast warming up their new contender for heavy-weight champion of the table-top fantasy role-playing game market. In the other corner we have Paizo, continuing to train their champion Pathfinder, who dethroned the D&D brand when 4th edition alienated too many of its fans.
Only one will leave the ring.
One of the issues that I think has either been obfuscated or just plain ignored is that more than anything else 5th edition is a response to Pathfinder. Whatever else WotC may say about including older editions in the new edition's design, they won't be a priority. They can't be. The ideological gap between old-school D&D and 3.5/4th is just too vast. There is no way to bridge that chasm. No, this is a heavy weight match for the big title. At the end of the day it won't impact old-school gaming in the slightest unless part of their strategy is to reprint older editions. Nothing short of that would bring fans of all editions back.