I'd love to see some isekai in a primitive and harsh world where MC knowledge would be usefull for real (make him an engineer or something so that he can design and build machines that would help his survival) No gayme machanics, no lazy fantasy. Maybe some kind of ancient civilisation/artifacts sprinkled here and here. Oh and a general steampunk/dieselpunk setting would be nice.
Isekai into another world as mysterious power in multiple people. People that have you pretend that you have feelings while you actually do. You watch people grow old and wars change countries as time goes on.