Why do people whine about the size of DSLRs? quality has to come at a price - even if todays best quality will be available in a GoPro-sized body, a regular size DSLR would still bring quality, that is that much better.
Also, this is just an early rumor - no one said it's going to have G1X's sensor. Proof is in the pudding - pancake 40mm points towards a bigger sensor (and no new mount?)...
It's about use cases. I think for most professional and a lot of enthusiast use cases, the size of a DSLR is more appropriate. For protracted use on a large job, with a big lens attached, the format of a "large" DSLR, with a portrait grip is the most ergonomic. IF you need higher quality than a DSLR can offer, you need to goo medium format.
For people wanting a compact camera, where size, weight, or obtrusiveness are an issue, a smaller system has a lot of benefits. This includes some specialist professional uses (probably mainly reportage). A smaller camera also has a lot going for it for street photography.
I think most people who want a small (mirrorless) system are not expecting the same IQ, focusing capability etc. as a 5DIII or a 1DX. Those who are wanting a mirrorless system for a reason other than upgrading from P&S are mostly aware that there is a compromise on quality relative to a DSLR.
For myself, I want a camera that I can easily take with while cycling, as I tend to be out and about a lot on my bike at sunrise and sunset, for air travel, and for situations where a DSLR is too obtrusive. I would probably settle for a general purpose zoom with IS and a few of primes (wide, normal and portrait). The system needs to be compatible with my current Speedlites (i.e. hotshoe is a must-have), and should have an adapter to use EF lenses for the odd occasion when I want to use a more specialised lens.