Curious what you consider a major DAW? Does Reaper count? In any case, I would be thrilled with Cubase for Linux and I’ve put my vote or comment in every chance I get. But if Steinberg doesn’t jump in to Linux… you do have options to use Linux right now.
As for many people switching over, I think it might be true once we reach critical mass with several factors coming into play over the next few years. The difficulty bar to switch to Linux has been trending down for years, the pro audio ecosystem has been maturing and growing, and Apple and Microsoft have taken a direction that might just push enough people to build that critical mass that will attract the biggest developers. Will we reach that critical mass to bring Steinberg over? I have no idea, but I sure hope so.
But there are already some excellent DAWs on Linux, as you know. I’ve been using and testing most of them for a while now and they work great. I wish Cubase/Nuendo were among them, but I will have to move on if Steinberg stays exclusively on Win/Mac. I have been holding out and wishing for Steinberg to join the Linux community, but my time is running out and I no longer want to juggle Linux plus Mac or (formerly) Windows any more. So I’m heading out the door. Microsoft and Apple have gone a direction I don’t plan to follow, so it’s going to be the end of the journey for me with Steinberg fairly soon, unfortunately… unless they decide to start developing for Linux, which I would welcome with plenty of upgrade fees for every product that gets ported to Linux. I don’t need everything all at once, but if I got some official signal from Steinberg that they’re developing for Linux, I’d be thrilled.
BTW, the two best commercial DAWs on Linux IMO at the moment are Reaper and Bitwig. Presonus has a Linux beta for Studio One as you already know, and that will be an excellent option when it comes out of beta. I imagine by Studio One 7’s release, that they’ll be ready. Right now the beta has some rough spots, but it’s pretty impressive if you think about how much work they’ve done. You also have Tracktion Waveform 13 Pro (which is surprisingly fun to use), Harrison Mixbus 10 Pro (which now supports immersive audio), Renoise (which follows a classic/retro tracker paradigm which might get you out of any creative funk you’ve been in), not to mention all the open source ones… etc…
So there are some excellent options now. And as far as plugin developers for native Linux plugins go, you’ve got some outstanding developers that cover a lot of areas from U-he to TAL to AudioThing and other gems, including great open source plugins. And for the areas you can’t cover easily with native plugins, then you of course have Wine and Yabridge, which work better than you might think, which allow you to run many Windows plugins in Linux. It’s not as hard as some people imagine. It’s not a mystery. A good percentage of my Windows plugins will run just fine on Linux. I use a lot of typical Windows plugins, including Fabfilter and I even now have Native Instruments Kontakt working well on Linux (although that was trickier to get working, but still not difficult).
Anyway, the time has come when it’s not that hard to make the leap. Everyone is different though. You have different needs than I do. But for me, I’m basically done with Windows and macOS, and I’ve been moving more and more into Linux, and it’s been a fun (albeit bumpy!) ride. The tough stuff is behind us IMO, the early adopters years ago helped pave the way. The road right now is not perfect, but at least no one needs to feel trapped in Windows or macOS any more.