I think the reason the SL1 was so unexpectedly popular, and why the SL2 will be so popular, is the target market is not a primary body. This shouldn't be the only DSLR you own. This solves a lot of complaints about people's primary DSLR while still letting them use all the expensive glass they own. For example, for someone who has a gripped DSLR, this provides something smaller. For someone who has a FF and wants extra reach, this provides a crop factor. For someone who wants something lighter, this provides about a 1.5lb weight savings. For someone with a FF camera that wants access to some of the ultralight weight EF-S travel lenses, like the 10-18 STM and the 18-135 STM. Or even for someone who has a wife who has smaller hands and wants something that will fit those hands better.
Yeah, in case you haven't figured it out I'm hoping this is the SL2.