If I could pick I'd make the cataclysm heirlooms look like :
Plate : DKT10 (Black/Purple)
Mail : ShamanT10 (Grey/Blue)
Leather : Rogue T8 OR T5(Purple/Black)
Cloth : Mage T10 (Black/red) or Lock T10 (Black/purple)
Rogue T5 for refference : http://www.wowhead.com/itemset=622
Rogue T8 for refference : http://www.wowhead.com/itemset=826
I feel heirlooms should include helmets to complete the aesthetic of it , instead of having a junky looking random helmet w/ your heirlooms whether the helmet would include another +10% xp boost or not , though imo it should
Weapons : They should ALL look like ICC10/25 weapons with the exception of 1 handed maces those should look like ToC10/25 ones
They should include fist weapons , a polearm , and shields this time
The daggers should come with 1 as main hand only (1.8) and one as offhand only (1.4 speed) to enforce correct ideas upon new rogues early on
Edit : This is ideally , what I would like... however realistically I'd prefer they just make them look completely brand new and not re-used old gear skins... (With the exception of gladly using Rogue T5 for the leather )
More Edit after being overly criticized for suggesting T10 lol