I don't understand why people ask stuff that would be impossible to fit in such a small body. Do you guys want a mirrorless DSLR-like body?
no, we want solid and robust mirrorless system cameras with better IQ and photographic performance than any DSLR at a fraction of the bulk and weight. Good thing is, there is no law of nature against it. Only the unwillingness of imaging gear suppliers to build it, as long as they can sell yesterday's crap like the EOS-M or various DSLRs.
To be miore specific: what exactly would not fit into a very compact mirrorless system camera body?
* really fast and precise Hybrid AF [contrast AF plus phase-detect Af on sensor]? -> no difference in body size/weight
* vastly improved sensor with much better IQ ... resolution, DR, low-ISO, hi-ISO noise? -> no difference in size/weight
* ultra hi resolution "retina" EVF with minimum 4k rresoultion? -> no difference in size/weight
* one front-whell, one rear-whell and 5 freely assignable, well-placed buttons? -> no difference in size/weight
* higher fps? focus peaking? 1001 useful firmware features -> no difference in size/weight
* magnesium-alloy body, fully dust- and weathersealed [IP 67] ? -> no difference in size, little in weight
* WiFi, GPS, Canon-EX-RT radio flash master built in? -> very little impact on size/weight
* built-in little fil-flash -> little impact on size/weight
* fully articulated "retina" 4k LCD screen? -> very little impact on size [about 1mm in width], little in weight
* battery good for min. 500 shots and decent handgrip? -> little impact on size, if properly done
* full frame 35mm sensor? -> some impact on size, but not a lot, if properly done (see Sony RX-1)
Even with all of these items built into a full-frame mirrorless cam, it could still be significantly smaller and also lighter than any DSLR.