here's what Nasu would do if he was smart:
as soon as Prillya's last chapter releases, the Prillya movie's release date is revealed and fgo will rerun the first Prillya event or add it to the rare prism shop
in conjunction with the movie's release, the second Prillya event will run
it will run for 3 weeks and have 2 banners
banner 1 will be
>SSR Berserker Beatrice
>SR Archer Angelica
banner 2 will be
>SSR Ruler Pandora
>SR Berserker Sakura
the event's welfare will be SR Moon Cancer Tanaka
the event itself will be a grail front that focuses on defending an objective from the Ainsworth family
you will have a tile you need to defend while Angelica, Beatrice and various shadow servants repeatedly try to overwhelm you
they will sometimes displace Sakura behind your lines to disrupt your defences
the final boss will be the pithos itself, forcing the player to send forward servants to disrupt it while still handling the never ending servants pouring out of it's mud
featured servants in the event will be Astraea, Rider Ishtar, Kid Gil, Illya, Miyu, Chloe, EMIYA, Bazett and Rasputin
Astraea, Rider Ishtar and EMIYA will receive skins that replace their appearance and voice lines with ones that make them appear like Luvia, Rin and Shirou