justa1972
I was a confirmed Fuji X-E2 (at the time) user, but also had a FF itch to satisfy, I bought a s/h 6D to scratch the itch (I previously owned other Canon DSLRs, and at the time still had a liitle Canon glass like the 50mm f1.8), whilst I could appreciate the low light capability, the weight options when I looked at decent glass really put me off (i did add some glass, 24mm oand Tamron 24-70) but I ended up trading it for an X-T1, and recently traded that for an X-T2. Now for my type of photography the X-T1 offered no limitations over the 6D, and the X-T2 is a definite step up. The low light capability of the X-T2 with the Acros simulation is astonishing for a crop sensor.
I think your upgrade should be driven by glass not body though, Fuji make some fantastic glass, and it sits very comfortably above the budget Canikon Glass, and some of it rivals L type glass. But once you are up to L type glass, or equivalent ranges from Nikon/Sigma/etc the weight (and physical bulk + cost) rises quite a bit.
I'm not the only forum member to chop in FF for an X-T1/X-T2, and we may not be right, or suit the needs of your style of photography, but upgrading to FF and then going back to Fuji will not be a cheap exercise, and Fuji's are definitely boomerang cameras!!!