I am guessing comic con at the same time as luke. Howard likes to make it rain to announce his arrival.
Wouldn't be shocked to see a ROTJ Vader revealed along with Luke and have all 3 in one section of the display.
That's been my guess also for a while. It's certainly time for HT to crank out another Vader, though I expected ESB first... but with Luke Jedi and Emperor both partly revealed, seems pretty likely for ROTJ Vader... unless they go the SS route and do a merging of ESB/ROTJ Vader with partial and full reveal helmet. But knowing HT, they want to milk Vader so merging two potential versions doesn't seem like they're style.