The current plan is to update Arcade Mode when we're done either with the winterland, or after we've finished up the Temple of Seasons!
I'm personally leaning towards doing both areas in Story Mode first, and then implementing them in Arcade Mode, because we're sort of "in the zone" with content creation right now and switching up tasks usually takes away some momentum.
We do know many players like the Arcade Mode just as much (some even more) than the Story Mode, so we'll make sure to keep it reasonably up to pace with the content progression.