I figure if they do more prime lenses such as the 50mm for the EF-M system it would make more sense to future-proof them by making them full-frame compatible.
The EF-M 22mm is somewhat similar to the EF-S 24mm pancake, so there's no reason why a EF-M 50mm couldn't be full-frame compatible for the future even if such a camera doesn't come out for a while. Now, if Canon were being smart they'd launch a 50mm for EF-M to take on the Sony/Zeiss 55mm lens which is stunning, rather than just repackaging the EF 50mm STM style glass for mirrorless.
Similarly, I can't see Canon launching a 24-70 f/2.8 EF-M zoom unless they also aim this at full-frame. And as much as I like it, it's going to be heavy.
An EF-M 17-55 f/2.8 would make more sense for APS-C, but may still be too heavy. Something of a compromise such as a EF-M 17-35 f/2.8-4.0 may be enough