The problem with mirrorless lenses really is with non-retrofocus lenses, especially wide-angle ones. The angle of incidence of light rays just gets too high, this si why I suggested a reasonable, not too short flange distance.
Personally, I'd like to get rid of the mirrorbox - EVFs have come of age, they are plenty detailed, and they even allow one to view things as they are outside, light level wise, or choose to see it as the image will be recorded.
As to aperture equivalence: I don't really care about that. One chooses a system for a reason. For extreme shallow DoF one choses a FF camera, or Medium or Large format. Besides, I don;t know whn you last shot a fairly tight portrait, but if you want more than a few eye lashes in focus with a lens normally used for portraiture, on FF you really need at least F/4 to achieve that, so an F/2 MFT lens will suffice, no problem.
If I really want very large apertures on MFT, I use my metabones adapters with my Canon glass, no problem, but in that case I specifically choose to do so.
I love FF shooting (own a 5D II after all), but I don't always want to carry it around when I am on the move, which is most of the week these days. And the IQ of MFT is very good indeed. In the end, in order to make a photograph, you need to carry a camera - and in my case I always do and want to do so, but not always a FF with the relatively heavy lenses I own.
Time will indeed tell what mirrorless FF will do in the market. The way it is now there are relatively few users, however. If Canon would come out with a 6D variant that is mirroless, I think uptake would become a lot better.
Kind regards, Wim
So, om one hand you want to criticise FF mirrorless for vignetting at large apertures, on the other hand you do not care about the large apertures when you look at MFT. Convenient .
Also, you complain about the loss of DR when we touch on correcting vignetting on FF, but you do not care about that MFT has less DR to begin with. You want to argue both ways, as long as it is in MFT direction, it seems?
I do not care about mirrorless and EVF much. it hinders my creativity a lot. I own no Sony FF mirrorless or MFT, I try to assess things honestly. Equivalence is a big indispensable part of that.
Oh yes, and I also do not care about silly big DR figures.
The 6D follow up will be a FF DSLR. It won't have the ergonomic issues of small mirrorless cameras, and maybe Canon will also develop a FF mirrorless camera, either with EOS M mount or with a wider mount. Time will tell.