You'll get JP in heroics like you would triumphs and their predecessors before. You'll get considerably more JP per dungeon than you do now at 80 as well.
Basically, if you're a) bored, b) still like doing all the WOTLK dungeons or c) an insane min-maxer, go for the soft cap, but there's really no reason to worry about it, and it won't give you a considerable leg up (a piece or two of blue prep gear at 85, basically, if beta holds).
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AC - Hokkaido Disco, Flesh Wound - retired
EQ/EQ2 - Straylight - retired
UO, DAOC, AoC, AO, CoH, EVE - retired
WoW - retired
Help me SW:TOR, you're my only hope