The tools for owning your Linux OS are strong enough that anti-cheat is pointless because they're just broken all the time and nobody wants a linux box they can't control at all.
The only way it changes course is an enormous rug pull that removes most of the differentiation between PC and Console gaming and you end up with Steam as a dying product unable to compete with either other modes of PC gaming or the dominant console players. (Sadly that's basically what I expect when gaben retires)
I don't think Linux is a differentiator for the Steam Deck. It's obviously essential as a technical foundation though, similar to how it’s essential to Android phones.
But locking it down with DRM won't affect gamer interest in the platform as long as the games are still cheap, plentiful, and run well.