The SL1 has my attention! (It is doubtful a 28mm or 35mm pancake could be made quite as small as the EF 40mm STM, but something in the same general size range might be possible.)
I pre-ordered the 24mm EF-S pancake lens to use with my SL-1 - which is already my favourite travel camera. That's effectively 38mm, or close to 40mm on a full frame. I have the 40mm already. It's an odd length for an APS-C camera but is good for some things, is faster than the kit lens and also makes a tiny backup lens for emergencies.
For travelling the 10-18mm is pretty lightweight, has a stabilizer, doesn't cost an arm and a leg and makes a very nice mate for the SL-1. Or at least it works for me.