Can you stack 4,000 honour and justice points for the release of MoP so you can buy a few pieces of gear as soon as you ding 90? I know you were able to do this for Cata release, I just wanted to make sure so that I'm not disappointed if it turns out you can't.
From a PvE point of view justice points are near useless.
To be clear :
1) Justice points rewards are ilvl 450 (same ilvl as blue rewards from dreadwaste quest/Heroic instance Quest)
2) You will have to be honored with Klaxxi/Golden Lotus to purchase items (honored can be reach a few days after 90 ding)
Or you will have to be honored with Shado-Pan/August Celestial (Requires Golden Lotus Revered so can be reach a few days (weeks?) more)
3) A lot of class can have a full 350 ilvl sets crafted quite easily
4) In any case, Heroic instance drop are 463 witha 476 epic on last boss, and you can also craft some 476 ilvl item from professions by using living steel (Cata truegold equivalent)
To sumup : Most players will have no benefits from justice points items when they'll be available to them. In any case you should have plenty of time to make 4k justice points before that.