I'm not exactly sure I understand the specifics of what's being asked for. But the general idea for the virtual scheme is the ability to reuse other scheme handlers easily.
So if they just wanted to authenticate using the exact JwtBearer logic, but do something different for challenge/forbid etc, the virtual schemes will be making that easier.
Basically virtual schemes won't give you any more extensibility for any existing auth handler's functionality, but you will be able to compose/reuse/mix and match them on a per action (Authenticate/Challenge/Forbid/SignIn/SignOut) way that wasn't really possible before.
Agree with @leastprivilege for the support of reference token.
Maybe an abstract bearer authentication handler, with a JWT bearer handler and a reference token bearer handler.
We are using from the same way both token (JWT within a secure environment, reference token for hostile environment like the Internet). As we have to audit security events, a common layer of events would avoid out of synch behaviour.