It just takes time to do, and given that it's been a long time since there were any "infrastructure" grants to handle student or faculty time to support adding

It just takes time to do, and given that it's been a long time since there were any "infrastructure" grants to handle student or faculty time to support adding those instructions, adding and debugging them just takes time that nobody has to take out of doing research. It also doesn't help that everybody who has worked on MLRISC has long since moved on to other projects, so when you find what you think is a bug in something core, there's really nobody to chat with about it, get feedback on where the right place to make a fix is, etc.