Loving the Endless games, but they are sadly two of the only three games I play without native Linux support. Nothing against having to Proton a game, but it makes the computer run hot in a way that makes me a bit a nervous... So let me ask: any chance that Humankind will have native support?

Your Linux fans are clamoring for it! There are literally dozens of us!! (Probably?)

The best way for you to voice your desire for native linux support is probably to use Steam's "platform specific wishlisting" feature, and encourage everybody you know who is interested in the game and runs linux to do the same. That will create a much clearer picture for us on whether or not it is feasible.

I will follow those recommandation 

Got select for beta but couldn't play because it wasn't support on Ubuntu. Though about buying Windows but didn't manage due to the short notice. Maybe next time

I played about 25 hours of Opendev with Linux / Proton without having even a hickup (I would have changed to Windows if there had been issues). So I think unless you change middleware, or add copy protection or anticheat systems, there should be no problem with later versions.