There's at least two years of work in there as Fabrice Bellard's side project. This would mean about ~10-15 man-years of full-time work for a small team of experienced engineers, which is about what it took for jerryscript:

https://github.com/jerryscript-project/jerryscript

Granted, the targets aren't exactly the same (micro-controllers vs very small lib), but benchmark differences are impressive:

https://bellard.org/quickjs/bench.html

That's a pretty standard range for high level consultants. Bellard can definitely bill well above that, if there are tasks that require his talent.

How much higher above $1k/hr can he bill?...

Someone like him wouldn’t be billing by the hour, but rather as a portion of overall value created. For the kind of non-trivial jobs worth his time, six figures at least.

Any FAANG would happily pay him a 7 figure salary if he was interested.

Normally I'd consider this hyperbole, but if I had the means I would absolutely offer it. He's a generational talent.

Can you really put a number on this level of skill and productivity?

The problem with putting a $ figure on it is that people who create free software create emmense amounts of value but don't capture even a tiny fraction for themselves. OTOH to montize their genius they need to help corporates do things that are not neccesarily great for society. Also a coporate situation may hamper their genius, although at this level he probably gets to call the shots.

Also a lot of useless consultants would earn that much, as would people doing shady shit, as well as many talented people so the $ comparison is kind of insulting.

Yeah... his current employer already does.

You assume he's optimizing for money.

Do you know who his current employer is (if any)?

He has his own company now with another partner (https://www.amarisoft.com/) where they work on and distribute the LTE software he wrote.

Well, the scrolljacking is evidence no one is infallible. ;)

Well, not all lazy HN commentary, like criticisms of 'scrolljacking' should be taken seriously. ;)

It seems like he works here: https://www.amarisoft.com/about-us/