Like in OSGi (shudder,) when looking up services from the ServiceRegistry, it should be possible to require that services retrieved from the ServiceRegistry be locked to a specific addon API version (via addon-dependency/classloader mapping.)

(A) -> (B, v1)
    -> Service 1

(B, v2)
    -> Service 1v2
    -> Service 2v1

A should receive only the instance of Service 1 from (B, v1)