It sounds like you’ve already made up your mind as you don’t like the Z8’s form factor, while the RVI seems like the perfect camera to you.
A tempting price won’t make you enjoy a body you find too big.
Some love the Z8’s size and weight and find it balances medium to large lenses really well. Others find Sony bodies too cramped between the mount and grip, plus their pinky finger having nowhere to rest. It's a personal preference and you are better suited with current selection of Sony bodies at the moment compared to Nikon offerings.
I also wouldn’t count on a Z7 III arriving within a year. Unless Nikon announces it, neither the camera nor that timeline is guaranteed.
If Nikon’s release pace bothers you and Sony offers what you want today, switching sounds more sensible than waiting for something that may or may not materialize.
Personally, I don’t hold it against a brand when an unpromised future camera hasn’t appeared.
Many Z8 owners have effectively ended up with a more capable camera than the one they originally paid for.