My rather pessimistic view: I don't think there is any chance at all while the game is in EA, and very very low afterwards since the first months after that will be full with content patches, then work on an addon. And then they will feel the opportunity or right time to take on a port has gone, if they think about it at all.

I would be fine with Larian having an eye on proton compatibility. This is a short or mid-term goal that is actually doable with very small effort.