They have already announced the new Kiseki game and showed some screenshots. It will be focused around some unresolved plot lines from Cs4, the screenshots/art show some characters from CS and the Crossbell games (some of them secondary characters like Gaiu's brother or Scarlet). The new MCs from the game seem to be a girl with pink hair and a boy with brown hair.
From the screenshots they shared, it seems to run on the same engine as CsII/IV:
Was CS IV that bad? I have only played the official English releases, so I've yet to play the new CS games or the Crossbell arc. Currently I plan to play Zero using the fan edit and then Ao, and later the NISA transladed games (I'm sure CS IV will come next year tbh).
I've mostly read positive impressions on the Crossbell saga and CS III, and mixed opinions on IV.