Now that getting games that use BattlEye for anti-cheat working on Linux (either native or through Proton) is much easier, an Ubisoft rep suggests people post in their forum to show demand for it.
In response to a post on their official forum asking about Ubisoft hooking it all up, the rep mentioned they can pass the feedback onto developers and that hopefully "other players will reply here in favor of Proton support and the development team may then look to implement it". It's not exactly much and a pretty bog-standard response but it's a reply nonetheless and isn't being ignored.
The thing is, this is just about playing Rainbow Six Siege on Linux with Proton, and it's not likely the developer would do it just for that. Now though, with the Steam Deck that uses SteamOS 3, developers will have to get it working if they want their players to be able to access their games on it. Right now though, like everything else, it all depends on demand from users and how well the Steam Deck sells.
In other Ubisoft related news, it appears that a new "Ubisoft Connect PC Client" has appeared as found by SteamDB's Pavel Djundik on Twitter so it appears that more Ubisoft games may come to Steam.