Question: can you set a version in a schema?

No. You could emulate it by naming the schema

schema_v1.json

,

schema_v2.json

etc. and changing the schema references in the policy to the correct one.

i am doing that right now, but it's a PITA to manage. Any plans to support this in the future?

You could also use subdirectories like

v1/schema.json

to organize them -- if that makes things easier. We haven't really considered explicit versioning for schemas because they usually tend to get shared a lot more and the changes are mostly additive in nature.