How do you handle schema migrations? If someone has thousands of JSON form definitions stored in a database and the component API changes, is there a migration strategy or versioning system built in?

I don't think there is a simple answer to that, if moving from a big project to GolemUI or any other platform, the key would be to do it iteratively, first starting with a POC and then slowly intaking the rest of forms, if you were to consider doing a POC with GolemUi we will more than happy to help with this obviously :)