After I hit lvl 90, I bought 3 pieces with justice points, that I already replaced the same day trough heroic drops. As raids are not yet live, I have to farm valor trough 5 man heroics. After raids are live, who is running heroics anymore? What happens to gearing alts and queue times? I have converted my jp to honor trough the cata jp vendor. I have no use for heirlooms, since all my characters are lvl 85 (we had plenty of time before mop). We cannot use jp to upgrade 5 man blues either. Trinkets and offhand are the hardest pieces to get as drops (only 1 caster offhand), the jp trinkets are horribad. You cannot buy mop materials either with jp.
You don’t need to do heroics for valor, you get valor from daily quests also. Heroics are completely optional. The celestial dungeons will come out in few weeks though, which have useful gear for most people.
Until realm restarts such changes do not propagate across all layers. Wait for the next reset or layer yourself. Only the layers which were active at the time the change was made will contain the updated vendor until the next reset.