Thanks for the feedback! I think/hope we are taking weeks rather than months. I have already a working implementation of checking the user-set rewrites here (
https://github.com/ory/keto/pull/877) and a draft of the parser for the language here (
https://github.com/ory/keto/pull/920).
As far as transitioning goes, the changes will be backwards compatible. So if you don't configure rewrites, everything will be have as before.