He's running brave now
From what I understand though, Eich has lost faith in Mozilla maintaining their own renderer, so if he came back to Mozilla it would probably coincide with Firefox becoming yet another chromium skin.
Brave is growing, has grown every month, not at over 5.5M MAU. I am not sure how to interpret "Brave doesn't seem to be catching on" as other than false. Firefox in 1H2004 was in a similar trendline. People then still said "IE for evar!"