So the weapon drops from Garrosh are now 90-100 heirlooms. Since WOTLK the final boss of the expansion has dropped weapons, only to have them replaced by questing greens/blues in the next expansion. The article says these heirlooms drop from all raiding difficulties except LFR, which means Blizzard intends for players who earn these weapons to use them while leveling through the next expansion. The way I see it this confirms ten levels for the next expansion; it the expansion was capped at 95 these heirlooms would be as well.
Great news! A Burning Legion expansion spanning ten levels leaves a lot of room for epic content.
EDIT: just realized there's already a thread on this... Damnit. Please lock, mods