Along with the greater frequency of 5-mans, we'll be seeing new Challenge Modes appear too, and they'll feature new rewards. I'm wondering what the rewards will be -- were the transmog sets and a little Valor enough for players to feel motivated to do Challenge Modes? Or should there be additional rewards for the most tricky of difficulties? Too much good stuff and they become "mandatory", too little and the proposed harder heroics will replace them.
We will have to wait and see what happens to the Mists Challenge Modes. Personally I hope they're scaled up to max level, or altered to reward big chunks of XP, or they will be abandoned forever. Bumped up to level 100, with new gear scaling added, they could continue to be enduring content for Warlords.