such forks already exist, it's just that very few people use them.
there is seldom very much disagreement on the performance impact, so 'real performance impact numbers' don't help much. the disagreement is in the value of the protection being provided.
As the article says, if someone can show a way to use one of these things in an exploit, the problem gets fixed fast (and a generic solution to the type of bug _is_ preferred when a fix like this is done)
but if there's not known way to exploit the vulnerability, or the exploit can only be done by the system administrator, there is a lot of resistance to impacting performance 'just in case someone figures out how to exploit it later'