If my previous issue of granular scopes are addressed, doesn't that also solve the discovery problem? The SMART Access Token response will contain scopes which tell the App what is possible in the current context. Similar comment on handshake requirements - the AccessToken is a handshake?

Existing Wording:

In the current proposal, we leave discovery out of band. For example, a client must consult server documentation to determine which message types a server supports. We welcome ballot comments that consider whether we should define an in-band way to advertise which message types (and possibly which parameters) a server supports (e.g. via added details in a .well-known/smart-configuration).