I am going to utter the most controversial statement ever to Touhou fans; I hate Reimu and Marisa. I always have, I always will and I don't think anything short of a total reboot of the series like with Embodiment of Scarlet Devil will ever give me a chance to change my mind.
That said, I would love it if more older characters were used in future games. Hopeless Masquerade for example, felt like a perfect chance to get Meiling back into things, and also Shou... but instead it was just a faith based brawler. Don't get me wrong, it was awesome to see Ichirin get some face time, but when you have a game based around gaining faith and you don't use Shou, an avatar of a WAR GOD as a fighter...
Or Urban Legend, it was great that Mokou(-tan) was brought back and we finally got Kasen, but they basically just reused the whole cast from Hopeless instead of giving some more older characters (LIKE FUCKING MEILING) a chance to come back and be of some use. I don't know, maybe this is becoming a trend, since Lunatic Kingdom brought back Reisen, so perhaps future games now will just bring back one old character every time.
... Yes, if ZUN brought back Momiji, Flandre and Koakuma, I would stop complaining. Mostly.