I like the idea of George as culprit for EP3, but for other episodes not so much. Same for Kyrie, but I could imagine her being part of it in EP4 too. She seems to die early in the first two episodes.
Do note that the ???? page is the next one right under the titles of Umineko and Higurashi. Could it be his new project?
What kind of story could it be, if it's When They Cry 5? He has done a village mystery, a closed circle island... repeating and endless train trip? Or maybe a hard-boiled detective story?