You sound like video is quite important to you, if this were the case then the 5D iv might be the best camera to consider, it has the low light capability of the 6d, Af said to be comparable to the 1Dx mk1, and a host of video features (including a rumoured video spec update to C-log).
However you would loose FPS rate compared to the 1d4 and possibly metering linked to af point, and also the flip screen.
They are all good cameras, each has its own strengths, my opinion is that the 5D4 is the best compromise of all of them in 1 camera.
The 5DIV may be the best, most versatile option. It does require me to sell all three current bodies. That would certainly take care of my 'too many cameras' problem. It also allows me to keep my wide and ultra-wide line up as is. The transition to 5DIV involves only switching bodies. I already have all the glass I need for full frame.
I think the only real question here is if you want a full frame or a crop camera. If you need the thinner DoF and extra iso range, then you're probably going to end up with a 6D ii, despite your statements about gaining nothing. If you don't need the aforementioned and like the unmatched EF-S lens line up then stay with the 80D. Sell whatever FF "only" lenses you won't use when you sell the bodies. I'd probably be in the 6D ii market my self if it wasn't for what it would take to replace my EF-S lens line up in FF. 10-18, 18-135, 55-250 and an 24 pancake. Combined it's less than the cost of one good prime and to replace it would cost a good bit and result in heavier and larger FF lenses with less focal length coverage that do the same thing. But, if you don't care about the EF-S lens line, and you want your 80D in full frame, that's what the 6d ii is shaping up to be according to all the rumors.
Your post is quite confusing. Why would I want to upgrade to a 6DII that offers little to nothing over what I already have? There is no such thing as a full frame "only" lens. All my EF glass works quite well on all three formats. I'd have to tetchedindahaid to sell good EF lenses for lesser EFs lenses, no matter what camera I am shooting. If I went to the 80D only, I'd sell the 12mm FE, 15mm FE, 12-24 II and 17-40; they are a bit pointless on apsc. A good, used 10-22 would cover most of my wide needs.
I've had the 10-18 it is crap, and slow compared to the 10-22. Sell a perfectly good 24-105 for a lesser 18-135? Sell a fantastic 70-200 f/4L IS for a 55-250 STM. Rethink those, please. The 80D is already the apsc equivalent of the 5DIV. Again, what I already have covers whatever Canon will put on the 6DII. Not going down that rabbit-hole.