The rumor says:
"new telephoto lens"
which could easily mean a telephoto lens design that currently doesn't exist as well as an update of one that does.
Why not announce a new APS-C telephoto lens with a new APS-C camera?
because there is no point in an aps-c telephoto
If there is no point in an APS-C telephoto then why does the EF-S 55-250 exist?
Because going as wide as 70mm on a crop camera is still quite tele, putting the lens out of general use for many people. 55mm at the wide end makes it more of an all round tele zoom for crop users.
Once you drop much below around 70mm in focal length, there are packaging and cost advantages to a smaller imaging circle than FF.
A 70-xxx, 100-xxx or 200-xxx has somewhere in the region of a 1% weight and size saving with the reduced rear element size required for the EF-S imaging circle - the lens elements further forwards are all identical in size. So why not just make such a lens FF compatible, and therefore sell it for less due to increased sales?