What I would like it to be is an option to LFR or LFD old dungeons/raids with old scaling gear, that scales to the current LFR item level or somewhat worse.
I wonder how fast the theorycrafters will find out those old forgotten hidden scaled gems!
For example on vanilla there used to be a godly warrior trinket from brd that gave you an extra attack. Would that trinket scaled be good enough to have any use on current content?
Or one of the most wanted items back in TBC was a trinket from gruul. How would that trinket scaled cope on current content?
Whatever it is, I'd say expect it in 5.3 or 5.4 in an effort to pull back subs.
"I quit WoW."
If I say it's Azshara next enough times, eventually I'll be right. So here we go again. It's got to be Azshara next, so get ready for the Sylvanas expansion we inevitably get instead!
Your idea could also incoporate a heirloom panel where once you get a heirloom you can see it in an heirloom wardrobe that is accessible by all your characters. No more sending by mail etc. would be great actually.
Anyways nice thinking, let's see what happens!