May be. We have not seen future. But that is not the point and a person who is claiming there is "zero evidence" is mistaking absence of evidence to evidence of absence. Arsetechnica has published several articles on this topic in past and are available to read on Wikiepedia page for the OS.

General information suggests this is one of those long term things if successful would be massively game changing.

Check the context. The person I replied to is claiming there's "zero evidence" Fuchsia will replace other Google OSs which is obviously wrong.