One thing that leveling really lacks for me currently is gear progression, alot of people are praising older versions of wow that questing and dungeons actually felt rewarding, it felt good to get a green or blue item after finishing a long quest chain, or winning the roll in deadmines.
With 7.3.5 which fixes one of the major problems of leveling I feel like it would be a good oppertunity to change up heirlooms to get that feeling back, like Ion said at blizzcon how raidtier set items locks in 4 gearslots of your character, heirlooms do that for 10 of your gearslots. While I dont think heirlooms are a bad thing, I think its a bad thing that 10 of your gearlocks are locked and there is not a single item that I have seen that is better than heirlooms at whatever level.
My suggestion is to transform Heirlooms into item enchants.
This way looting gear while leveling will usefull again,
You dont have to spend tons of gold for each different armour type,
Your character doesnt look the same from lvl 1 to lvl 110,
The enchants will atleast contain an EXP buff,
Your friends wont get mad that you do have heirlooms and they dont, because you can enchant their items too just like how enchanting works right now,
Other (new) players wont get obliberated when entering a battleground or dungeon.
It also fits more into the game fantasy IMO, right now pulling infinite overpowered items out of your butt at level 1 feels really dumb, but enchanting items with spells and wisdoms that you earned on your higher level character isnt so bad.
Id like to hear your opinions or different ideas
EDIT:
Discussing DESIGN of heirlooms, not wether I LIKE them or not