I think that mirrorless is a sort of revolution or at least the evolutionary equivalent to the Cambrian explosion.
You know, punctuated equilibrium and all that.
I think the move to on-sensor AF is revolutionary. And while it isn't yet up to good DSLR standards in terms of speed, it is in many ways more accurate overall than other more conventional systems when it locks focus.
I don't buy, however, the whole WYSIWYG argument via the EVF. Even the best EVF is a horror outdoors in daylight. Try WYSIWYG-ing to open up the horribly blocked-up shadows in the EVF, using your exposure or comp., and see what the file looks like. In this regard, EVF/mirrorless has a LONG way to go, IMO. It is good enough to "tolerate and work around" but nothing more. And I don't think having the plethora of on-screen information compensates a bit - in fact I often find myself turning it all off so that I can see "what's out there" enough to make a decent composition.
What I can say is this, even with "big lenses" on my Fuji X-T1 (e.g. the 10-24 and 40-150) the direct comparison in weight and bulk in "angle of view" equivalent for my FF system yields a HUGE difference that "pictures of them side by side" does nothing to illustrate. The FF is massive in-hand and very much bulkier and heavier.
And, I just completed a comparison test of my 20+ MP FF gear against the Fuji X-T1 in print sizes up to 17x25 (as large as I usually print w/o having stitched frames) and the Fuji is easily the equivalent and in some instances better in tonal transition and detail rendering.
And, I have from 15mm to 320mm equivalent range in lenses, and two bodies w/ battery grips in one small backpack style bag. It isn't "light" but it is a heck-of-a-lot-lighter and way less bulky than the two bags required to contain my equivalent FF system with only one body.
Horses for courses, of course.
And, finally, these days when I need the "big gun" in terms of resolution and detail rendering, I reach for one my three stupid little Sigma DP Merrill cameras - which kick butt on both the APS-C system and the FF system (assuming that I'm using them like mini tech cameras - SLOW and deliberate).
It is a wonderful world we're living in as far as technology goes. I'm glad I've lived long enough to play in it.
Rand