My main attraction to ML, being photographing exclusively people, was the improved AF systems and the face/eye focus (consider that I was coming from 8 years of a 6D, so a very rudimentary AF system); slightly reducing size (just partially; I actually enjoy "big guns") and weight would certainly be interesting, but actually I'm still relatively young and I still can handle big guns pretty well, so I see it as something I would enjoy in the future, but now I don't really care. Either I work in my studio, or I'll reach a (event) location with my car, I don't walk/travel for extensive periods with bags of gear on me, so size/weight is a no issue as now.
I can tell you that just the new AF really improved my photography, because 90% of time I don't have to deal with it, I choose subject and then the camera is taking care on its own, and I can much better concentrate on composition and in capturing the moment; I'm much more "into" the event, or much more in connection with my subject(s) in a portrait/headshot situation, I have more "processing power" of my brain assigned to direction of my subjects, with much less distraction on dealing with the tech side.
Also being used to shoot wide aperture primes in natural light, or mix light scenarios, the hit rate on close shots due to narrow DoF had drastically improved, and I now extensively use Servo, that I was rarely using before in DSLR days; just that pays for the move to ML for me.
Every euro spent on bodies and cameras has to return back to me, so now finding good deals on EF stuff is doing it good for me; I also happily shaved off lot of stuff that I was barely using, and I rationalized my entire gear, so in some way I had actually reduced the overall weight of it all.
Next move will be getting rid of adapters, but that means third party, and most likely USED third party, so the sooner third parties will hit the market, the sooner they will end up in the used market after some years; that's why I'm in a rush for them, as even if today all third parties will present and deliver RF stuff, I most likely will have to wait 3/5 years for the stuff to reach the used market at a price I'm comfortable paying. So that's why every day passing without third parties is a bad day for me.