The OM-D E-M5 Mk III is almost(*) the perfect second body for me (my original E-M5 is not retiring anytime soon) but I plan to wait for the street price to drop, as it seems to do with Olympus in particular. The addition of PDAF is itself almost enough, as it should make my mix of MFT and Four Thirds SLR legacy lenses more agile, and the weight advantage over the E-M1 Mk II is an advantage, especially with the plan of sometimes carrying two bodies so as to have two lenses rapidly available.
I am not sure why anyone thinks that a jump up from 20MP is much of a priority for this category of camera, and with APS-C and 35mm format still offering new models at only slightly higher 24MP (or even 21MP in the case of the Z50) multiple major camera makers seem to agree with me. I would expect that the great majority of photographers using a small, lightweight system are not particularly into displaying images at much beyond "normal" size; that is, viewing images on-screen or on-print from a distance significantly less than the image's width. So I am still of the old school that for all but a tiny niche of huge print-makers,
"more than 12MP is for cropping and loose framing of moving subjects,
more than 16MP is for heavy cropping, like when none of your lenses is long enough, or you can't get close enough".
And for that pushing of telephoto/macro extremes, it is no use at all to have more but bigger pixels in a larger format and then cropping away a larger portion of them. I'd put my money into a longer lens and/or a TC before going for a bigger sensor and bulkier system.
But I will not make any claims for the 50MP tripod-only sensor-shift mode; most of my subjects are not static enough, even when they are flowers.
(*) To avoid sounding too much of a blind fan, my perfect bespoke camera would have a bigger battery in a deeper hand-grip, since that would still not protrude as far as any of my lenses, so would not have any real adverse effect on bulk. And maybe a bigger EVF magnification — but I zoom in on the EVF for critical inspection anyway, so that is not much of an issue for me.