Keep the G80 and get a D700.
That's what I'm thinking about.
I love my G80, but fancy trying FF.
Nothing wrong with that, the D700 it was a great camera, I almost bought one years back but was lucky to get a bonus from work at the time and was able to buy the D800E when it had just come out. I had some nice lenses to boot too and was happy with that for about 4 years. The weight was killing me though, I had back surgery around the time too and often my camera bag was hitting 10kg - I know this because anytime I flew I would weigh it to make sure I could carry one. Had some hefty lenses like the 24-70, 70-200 VR and 300mm F4 and I think my bag alone was about 3Kg. If you are getting the D700 seriously consider the Sigma 35mm 1.4, that was my favorite lens for Nikon, so, so good ... though you may need the dock to go with to calibrate, one thing I hate about dslr! The other obvious choice IMO is the excellent 85 1.8G, just get it used, very good value and an extremely sharp lens.
I am seriously considering a Canon EOS RP along with keeping the G80. It makes sense, because I have a couple of Canon lenses that I adopt to the G80 as is, with an AF adapter. So any lenses I buy can be used for both [I would be using EF lenses for the RP mostly, [though may go for that juicy RF 35mm 1.8 macro at some stage] I put it off for ages because of all the bashing the RP gets online - but that's all from videographers, I don't care about video, and I don't care that the DR doesn't match a Sony! It will be very good at higher ISO, just as the 6DmkII is.
My other fancy is a Sony A7RII, but the lenses I would want for a Sony are pricier and though that camera would be like a D800E in mirrorless form + on steroids, the RP has touch screen as good as the G80, it has the flip out screen also and comes with an EF adapter from the off for about the price of the Sony A7RII body only. Tough decision, and no doubt I'll watch another 100 reviews before fully deciding, it's a bank holiday weekend so have the time to do so
But TL;DR, yup, I will be keeping the G80 for now. I also considered upgrading to the G9 and getting a new lens but tbh, when you really look into it, the G80 isn't missing all that much that the G9 offers. Sure it's a much nicer body and has the newer sensor, but I've watched dozens of side by side comparisons and there's very little in it