About time-loops:
I doubt there will be something like this. My guess is that Eirin's medicine revealed that the Lunarians where planning some sort of attack against humans and youkai (Maybe to get revenge about Yukari fooling them in CiLR and SSiB?), and sent Reisen to do something aout it.
I hope there will be at least one of the Watatsuki. If not Yorihime (too strong, cheater, etc), at least Toyohime. As the Phantasm Boss perhaps.
Not because i like them a lot, but given their positions, they are more or less Yukari and Reimu's equivalent on the Moon. And because Reisen was their pet.
Also, first Mokou in ULiL, now Reisen. ZUN is really bringing pre-MoF characters back. I'm happy.
Full-power Letty and EX-Rumia when :V