Nope didn't answer my question. I know what you have dude 'cause you already told us. I asked if you were looking at replacing it, or, building a separate entity. You still haven't answered.
However I will try and approach both scenarios.
1. If you were looking to replace a 1080 with a Vega 56 I would have to ask why. The 56 is about as fast as a 1070, only it gets a lot hotter and guzzles down power. It's one of those things that only a mother could love. Unless you have water for it (to shut it up and stop it dying from heat) then avoid. Well, unless you are dead set on using Freesync which would be the only rational and logical reason why you would hobble yourself and downgrade.
2. If you are building another rig with another monitor and really fancy a Vega GPU? yeah that would make more logical sense to me.
Now. I am not sure what you are intending to do with the monitor either. So you've had enough of a 35" and want to downsize to 1440p 144hz? or is it going to be a separate PC for another use?
Personally speaking I would jump at it. Mostly because the res you are using is not 100% supported by 100% games and I stopped playing the "Hope it gets supported !" game a long time ago. I realised that the only thing they cared about was taking my cash, then once that was done I was cast aside like a used johnny.
As I said though, in any circumstance I would only ever pick a Vega GPU (and it wouldn't be 56) over a 1080 if I were absolutely desperate and wanted Freesync to work. And even then I would need to question my sanity, because the 1080 has both Fastsync and Adaptive. Which is usually enough for any one.
