Related to that, the ending of the 3.0 Amphoreus story (e.g. this stream from Camden Sutkowski (Aven's EN VA), at the 10:14:20 mark) has March's hair turn greyish-white like Eileen's, hinting that Eileen may be related to both March and Cyrene.
Shouldn't have installed a hot plate in the counter if you didn't want your fancy cafe to turn into an okonomiyaki joint frequented by all the truck driver ossans.
It only just occurred to me thanks to the commentary here (assuming I've interpreted it correctly) that, if you combine certain somewhat common headcanons about Sakuya's background with RemiRei, then yeah, you end up with Sakuya becoming effectively Reimu's step-daughter.