I think you're mistaken that marketing (in the sense of community building) is an important component of designing a language people would still care about in 1

I think you're mistaken that marketing (in the sense of community building) is an important component of designing a language people would still care about in 100 years. The history of the Lisp family is a counterexample. For 50 years (except arguably for a brief interlude in the 1980s) Lisp was popular only with a tiny community of eggheads. Now thanks to Clojure Lisp is fashionable. The history of such fashions also contradicts your claim that you can lock in a position of leadership by building a big community around your language. There has been new hot language every 5 years. First Perl, then Python, then Ruby, now maybe Clojure. The way to make a language popular in the short term is build buzz and libraries, because that's what the average programmer cares about. But to build a language that turns out to be the ancestor of whatever people are using in 100 years, you have to appeal not to programmers but language designers. You have to create the ideas language designers want to copy (have to copy, because you found the optimal solution). That's what McCarthy did.