How would the mainstream view it?
How would software support improve?
How would gaming look like?
Which country will become the first Linux majority? India? Seychelles?
How many local governments would start adopting it?
What year do you think it will happen in?
How would software support improve?
Basically fix the few things that work better in Windows, even for power users, ideally without sacrificing the flexibility that makes Linux so awesome.
Edit: bonus suggestion though this one is kind of tricky to do without sacrificing flexibility:
Less fragmentation between distributions. Recently I had some driver problem (can’t quite remember what) and googled a solution. I found a solution in a support forum for a different distribution than what I had. Looked good but in the end it didn’t help me because the config files were in completely different locations, default configs were different, packages had different names and they recommended using some UI tool to configure the device that wasn’t available on my distribution or at least I couldn’t find how to install it.
For myself, I’ll eventually figure that out. It takes me a few hours that I could spend on something productive but whatever, we’re geeks, we do shit like that. But now imagine my mom calls me about that problem. She probably won’t have the same distribution that I have because we have entirely different use cases. Good look troubleshooting that over the phone. With Windows, I can rely on 80% of all users having one of the latest two versions (so currently 10 or 11). The fix that works on my machine will probably work on theirs and most things I find online will apply to what they have. Same for macOS.
Edit 2: For context, I run Ubuntu and Debian on quite a lot of headless machines such as servers and embedded stuff. It works great and I wouldn’t want to miss it. But on desktop, I’m still in Windows and won’t leave for the foreseeable future. Every few months I try setting up some desktop linux and every time it takes less than a week to annoy me so much that I’d rather wipe the whole thing and install Windows than figure out how to fix that mess of two different display servers, five different desktop environments and two entirely incompatible GUI frameworks in a trenchcoat.