A high-end R7 isn’t going to put a low-end M50 “out to pasture”.
A high end R7 is only the first of a line of R-ebel line of cameras (RXX, RXXX) that will soon follow. Canon produce the R7 to allow 7D users to get the camera they were longing to get in the 7DIII, but rest assure that e R-ebel will come soon as well after the R7. Since the R7 and the R-ebel will be able to use the EF-S glass (with a converter) it means that those people that have a good line of EF-S lenses, will be able to use them for longer than expected.