Assuming this works and everyone remains happy with the Raid Finder system, is there a future for the Raid Finder model in the Dungeon Finder system? We know now that Blizzard has entirely revamped the 5-man system in Mists of Pandaria, offering new PvE encounter zones, timed instance runs, and no normal versions of level 85 heroic dungeons.
But what if Blizzard decided to follow the Raid Finder system instead and redesigned 5-mans with three tiers of difficulty? The first tier, the Dungeon Finder mode, would be designed to be easy enough that five puggers with no voice chat could queue for it and win. Normal mode would require five dedicated players working in coordination with one another but would still ultimately be easily conquerable without significant effort. Heroic modes would require hours of wiping, retuning of strats, and a dedicated group of players.
It's very likely that this is an impossible dream, that it's not really possible to design a heroic Ragnaros-style boss encounter that is as difficult for five players to kill. It might not be possible because 5-man groups have such varied compositions that certain buff and debuff compositions would make balancing an exercise in futility.
Excluding balance issues, would you play it? Would you prefer the option of being able to fight heroic Ragnaros with your four closest friends, knowing that it took just as much effort as a 25-man kill of the same fight? Would you rather leave raiding to raids themselves and keep 5-mans as they are now? Or are you looking forward to Mists of Pandaria and the new model of 5-man encounters we're going to be playing?