If we can make a patch for this on trunk, then Dio5 / Blackdog can apply it to their own branches before the next release.
For example, I use jQuery, so it totally sucks to have prototype imported and used to validate forms when there is an excellent jQuery Validitor plugin that is very easy to template and would add very little overhead to my existing pages. If the hooks were available, devs could produce jQuery/Mootools/YUI ports to perform these common tasks.
If someone is already doing this, or there is a workable solution already, please let me know. Otherwise I'm interesting in helping produce such a framework if someone wants to point me in the right direction.