Interesting, thanks. Is there any way to find out if a pool is using a modified stratum implementation, apart from asking the pool dev? I'd ask BAN myself, but they seem unable to answer even a basic question.......
All you can do is ask.
I think the bulk of the pools out there run variations of the major pool software available but no doubt a few run their own custom software. I've currently been working on my own pool implementation in c to try and redefine how a pool should perform and have posted a solo mining pool solution as a development prerelease and there will be a comprehensive regular pooled mining solution presented shortly, but my code is all open free software so I expect new (and some old) pools may come to start using it in the near future as they hit limits with existing software solutions.