Our current discussions around the round table (it is actually round, I am not being clever) have been over the possibility of alienating fans purchasing 3.5 versions who then have to upgrade to 4.0 versions later. Eventually, it is a safe assumption that all major developers would drop their 3.5 lineups for 4.0. This is, of course, assuming 4.0's rules and OGL are compatible with these companies' interests. Those that alter the 3.5 rules in a drastic way that can't do so with 4.0 have no reason to switch. But others, I imagine, would go exclusive 4.0 rather quickly (within 14 to 18 months being my guess).
Our intent is to release with 3.5 now, fully formed like Athena from the head of Zeus, and then release a 4.0 update (like a patch file) with no art and a basement price (next year) for those with the 3.5 edition who want to use the 4.0 but don't want to feel cheated to pay the full price for a replacement book. We could then issue a 4.0 complete edition if the sales warrant it. Whether or not further publications remain with 3.5 would depend on the compatibility of 4.0 rules and the sales of the 4.0 edition. However, it is a stable strata to base an argument that in time, those who love the 3.5 system over the (let's be honest) WOW-inspired 4.0 edition may feel dejected that no major company will release for the old system.