None. I didn't say Notch can't ship a blockbuster game (and he can ship exactly one). I said he can't code worth a damn, and should not be idolized for his prowess.
Go and get developers at various companies. Not necessarily game companies, get someone that is payed a salary for "coding".
Give them some rough specifications (for example, a simple maze, simple lighting) and ask for Dart/WebGL to be used, and a timeframe of one month.
See what happens.
Based on my experience, 5% of developers may present something like it.
So, ok, Notch may produce spaguetti code, bugs, etc, but he's probably in that top 5% of developers. (Which is also debatable because someone may be good at, let's say, web development but couldn't code a game to save their lives)
I've worked with developers like Notch. I like them because they can create rapidly iterate apps/sites/ideas that normal people/users understand and critique. Then developers like me come in and polish the turds under the covers so we can ship and maintain.
He's not writing SQLite or Space Shuttle code, it's a amusement.
Do you think Minecraft requires a complete rewrite to be maintainable?
They are working on rewriting substantial portions of the codebase, but unfortunatley Notch didn't hand it off to the most skilled maintainers and they aren't making things much better.
There is a clear separation between code quality and shipping a successful products. Ideally you would want both if possible, but a product is not just code.