IMHO Sony's goal is NOT to sell you a full frame mirrorless to use when you want a small camera, their goal is to be beat Canon / Nikon's image quality and have that be your primary camera. Canon and Nikon treat mirrorless cameras as a nuisance that keep people from buying their expensive, and presumably highly profitable, pro level DSLRs, and it shows in their mirrorless product offerings.
I am sure I am in the minority with this, but 20 MP is just fine for me. I don't want enormous files that cause me to need even more storage capability and better computer(s) to process the files. I also don't want to have to buy better, read: more expensive, lenses required to get another 5% out of the 36 MP or 40 MP camera. I don't approach digital photography as an arms race. Good enough is good enough.
Dave