Current Blizzard Idea is good but will be shattered by New Blizzard Guild System. Guild Dependance and Bonus for guild experience will dominate above bonuses from Dungeon Finder. The Only Way as I can see will works is to Make something really good and independent from current system. It can be Achievement and that can be obtained only in Solo running Heroic DF and has to be well rewarded with something unique.
Sample: Noble (Tank, Healer, DPS or other title) provided for 1000 (or .... other number, it case of common cense) Solo Heroic Dungeon Runs. Main Prize: Ashes of Al'ar.
Only way like this can make real burst of Tanks and healers because Ashes of Al'ar really deserve it. This will be real motivation for anyone.