The founders won the lottery, the language most likely will never make mainstream.

Ha! I think whether Mojo will make mainstream or not is already a forgone conclusion. It solves too much of a technical problem to be niche. To me, it is a matter of when... not if.

It is not the only solution to that technical problem though. Past attempts at this have shown a clear preference for solutions that actually are extensions of CPython rather than distinct tool chains.

Past attempts at what exactly, I'm not sure I follow. Are you talking about two-language problem, heterogenous compute, or cross-platform accerelated compute stack?