I don't think that is necessarily out of the running yet. OS development is expensive and low profit. Commodification may be inevitable. Control of the shell and GUI, where they can push advertisements and shovelware and telemetry on you, that is profitable.
So in 20 years, 50? I predict proprietary OSes will die out eventually, balance of probability.
This song messed me up a while. It hit a real chord,pardon the pun.