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?
Probably will be most notable for personal desktops with increased software support of consumer hardware. Mainstream only cares about what OS is pre installed, linux users are 99,9% advanced users just by the fact that they take the time to install an OS. Company adoption have the same issue, companies use what have worked before and what most employees are used to… and of course, what is pre installed on the desktops they buy.
Desktop linux is unlikely to happen at any point, just by the above facts. I am also not convinced it is the first choice for most tasks on a desktop. Servers and mobile it works great and other LTS hardware. With that said, I think when governments adopt linux we will definitely see an actual market and ecosystem develop… 2030? Maybe before, because countries will wake up and release its not the best idea to share all their data with MS. I could see something like Trump becoming president again, could actually spur on the adoption rate.
Sorry for the ramble, interesting question 👍