Are heirlooms a good idea?
It occurred to me that there are generally two complaints from experienced players about the early game that was revamped in Cataclysm: it is too easy; and you level too fast.
Now, I'm not saying that heirlooms caused these problems at all. But it's pretty clear that heirlooms make these problems worse. A character decked in heirlooms is significantly more powerful than a character in quest greens, and has a much higher rate of XP gain.
Cataclysm made the leveling game easier for new players. At the same time, heirlooms made the leveling game even easier for experienced players. I think the combination has proven to be excessive.
Additionally, I think heirlooms have created a couple of other problems. Low-level PvP is very affected by the disparity in power between a character with heirlooms and one without. As well, heirlooms remove much of the "upgrading gear" game while leveling. You never replace your heirlooms, so you never experience the thrill of getting a better bow or chest piece. I think that does suck a lot of the fun out of the leveling process.
I wonder if the Death Knight solution would have been a better way to go. Rather than speeding up leveling for someone who doesn't really want to level, maybe it would have been better to simply allow them to skip the leveling process.
You could sell a level 80 character to someone who already has a max-level character. Either for real money, or put in a way the max-level character can earn the extra character. But if you liked leveling, you could still level the old-fashioned way. It would be easy, but not as easy as heirloom-assisted leveling is.