[irrational]

The biggest impedances I see to replacing JS are:

1. You've got to keep JS around for backwards compatibility for the billions of websites already using it.

2. You will need to two engine teams, one to maintain JS and one for the new language.

3. Now you have a whole new vector for security issues. You've made the threat surface much broader. So, you will probably need to hire additional people.

4. You need to coordinate with all the other browser makers so everyone rolls out their new engines more or less concurrently. Other than experiments, nobody is going to start using it unless it works on all the major browsers and platforms.

[hajile]

That depends on the language you choose.

If we went to a scheme dialect as originally intended, we could have just ONE language for all the things.

Legacy JS? Just compile it into Scheme and run it.

HTML? Use S-expressions and support legacy HTML syntax by compiling it into them. Now you get all the power people want from template languages, but baked right into main language itself.

CSS? No more weirdness like adding sin() or calc() to make up for shortcomings. Once again, you get the power of the full Scheme language right there.