Not even with WINE?
It's a shame that Nexus Mod Manager has fallen to the doldrums. Curse and Steam are the only two realistic options for mod management. I prefer Curse because you can use different modpacks, different game versions, and different accounts. With Steam, it would be impossible to use a camera account, without re-activating HyperVisor. Curse (Twitch) gives a massive amount of flexibility, which is exactly what you need for these games. If I'm on a multiplayer server running 1.12.8, and I want a sandbox world in 1.12.9-rc.1 for mod development, and carrying on my 1.12.6 SSP with different mods, complete with the ability to use a camera account for third person timelapse videos... that's only possible on Curse.
VS could include a launcher manager that offers all of this, but it would still be all in-house, and wouldn't bring in any new footfall. With Curse, and Steam, you get the potential of millions of new customers, instantly, at no extra cost. You also save yourself from being the first line of tech support for the platform. All of the "hwo i intsal yr sftwr??1?!?" emails get sent to Twitch, not to here. It would instantly integrate the game into the live stream community, which is fast outpacing YouTube as a gaming platform. Let's Plays are still the best "Try before you buy" method of introducing new players to a game, and so everything to make that as easy, and seamless as possible is good. Being able to launch the game, and manage it all through the Twitch Launcher is the best possible way to do that. Linux users... well, there can be a bespoke native launcher in with the game as well. Linux has always been clunky, and unelegant compared to Windows, when it comes to stuff like this. As Twitch grows to take over from YouTube, they may expand their platform to Linux as well, in which case, you'll have automatic support there as well. That's up to the Live Stream community to put pressure on the platform to expand though, and for game developers to do the same. Facts and figures are needed for that, but the vast majority of users will be using Windows, and will have access to Twitch, and Steam, and will automatically know how to use both platforms.