Heroic old instances is definately a great idea. I fear the lashout of "WTG recycling old content Blizz" from the playerbase though.
in my opinion, next expansion needs to be Arthas blowing up the old continents and everyone fleeing to Shattrah as refugees. Gives the Dev team an excuse to revamp the old world for flying, redo the old instances as heroics (L90? what ever)... and a great way to introduce starting any class at 55 at the new "refugee" starting zones in outlands just like the DK starting zone.
but yeah, heroic VC or even better.. Heroic SM. i love SM.