I'd like to see something like an AE with themed challenges and fighters (probably featuring / focusing on the ones in the matching Holiday Relic), and maybe have the map be like a 'tree' shape; where it starts at a difficulty somewhere around Basic at the bottom, and goes up to AE levels around the top, with treasure nodes sprinkled in periodically so every skill level gets a chance at some nice rewards.
I just worry about them overlapping too much with the PFs, since those tend to be pretty grind heavy. Maybe if they followed the same schedule as the Holiday Relics so there's enough extra time to get them done before the PF?
Also a little stuck on what to offer as themed rewards. Yeah, some Essence Shards and a few Holiday Relics, but what else could be added in? I'm assuming the rewards will be similar to the PF Milestones, but is there anything we could do to make them distinct so that it's not just more of the same? Keys and Skill Points maybe?