My question for both Dragonlance and Dark Sun would be: What Era?
There's a big down side to the re-releasing the Prism Pentad (if they do relaunch Dark Sun): They're less likely to pretend it never happened. That's lousy.
On the other hand, there's a chance that the Relaunch would involve a short timeline jump and a new BBEG appearing and taking over Tyr, wiping out all those "Free City" ambitions in the process. That would get things back on theme nicely. He doesn't even have to be a Dragonking; maybe some cabal of evil Epic Psionicists (as opposed to those uselessly True Neutral ones). But a new Dragonking would be fine with me too.
As for Dragonlance, I would take it as a really good sign if WotC announced that 5th Age was actually just a really lucid LSD-enhanced dream of Tasselhoff's, and that the setting was being wound back to shortly after the conclusion of Legends. That would probably work for the majority of potential Dragonlance fans too, seeing as how the original trilogies are the best selling and most widely read. For the average reader jumping from Legends to a post-5th Age setting would be confusing in the extreme.
I think one of the best things about combining Dragonlance and 4E is the rules support potential for playing in different Ages. Now that you don't need Clerics (any Leader will do) you can play in the Age of Despair. All sorts of Ages and "settings within the Setting" can support play with the appropriate mix of classes ("Wizards are outlawed? No problem; who's gonna be a Druid?").
Man, I'm getting excited just thinking about it.