You’ve pretty much hit the nail on the head @Kelvin – I think that’s the exact overall tech industry defacto thinking that Evan is discussing.
“Well it worked out for these people, that’s just the way it’s done, so just carry on, make sure you open source everything, and if it turns out bad for you, your career, your family, your ability to compete/commercialise… 
weird dunno [some other project] seems fine”.
The takeaways stem from Evan’s personal experience as an independent language author, not necessarily generic commentary on all open source (even though I think lots of the challenges generalise).
NB: remembered Evan has spoken directly about Linux before in this same context.