Just a musing here. I am fortunate to have a nice collection of photographic gear (getting old you see - no mortgage), and have a Nikon D810, D750 and D7200, but also have my lovely EM1, EM5 II and LX100 M4/3 system with good Olympus and Panasonic glass.
I had a sort of epiphany the other day, when I was bemoaning the apparent lack of resolution in the EM1 and EM5 II with their measly 16mp, where M4/3 seems to have been for years until the new 20mp sensor came out recently in the GX8. Then yesterday, I went shooting with the D7200 and a "walk about" DX lens I had - the Nikon 16-85 VR, which back in the days of the old D300 was a decent lens, but noticed yesterday It's really starting to show it's age on the 24mp sensor of the D7200, and images taken were OK, but nothing special with sharpness average at best. It seems my DSLR's really shine only when very good glass is on them (for instance my Tamron 24-70 F28 VC, or my dearly departed Nikon 17-55 F28).
However I've noticed that no matter what lens I shoot with on the Olympus cameras (be it my cheap kit 14-42, 12-40 F2.8 Pro, 17mm F1.8 etc), they all come out tack sharp, and it's difficult to get an image which isn't' usable (unless I screw up). I don't know if this is because M4/3 lens have fewer lemons and are better QC controlled, the AF is more accurate on mirrorless (albeit maybe not as quick in continuous AF), if it's the IBIS, or a combination of them all.
I really think that if Olympus (or Panasonic for that matter), could defy the laws of physics and design a 20mp+ sensor with really clean ISO3200 and good ISO6400 (so about a stop to a stop and a half better than what we have now), I think I could finally drop the DSLR system altogether, however as it is, shooting long lenses (like the Panasonic 100-300 @ F5.6), requires pretty high ISO in the UK winter light, and the quality compared to what the Nikon's do at the same ISO's is a little lacking. Obviously lenses like the new Olympus 300mm F4 would give me a stop back but at over £2k, it's a serious lens investment for M4/3 especially when I have that FL covered in Nikon lenses I have. The panny 100-400 is probably going to be a great lens as well but again, is only F5.6.
Any body else think that the system is about 8 to 9/10ths there, and that the final piece of the puzzle is better CAF (although it's currently by no means disastrous), and a little better high ISO coupled with a little more resolution, and it would be a killer system. (even as good as it is now). As it is, I will continue to use my little Olympus bodies for everything except where high ISO or more resolution is required, when the Nikon's will take over.