If a user on 4.1.0 wants to create an emuNAND with a copy of 1.0.0 and boot into that, we should support that.
If a user on 1.0.0 wants to create an emuNAND with a copy of 4.1.0 and boot into that, we should support that.
If a user on 2.0.0 wants to boot into linux, we should try our best to support chainloading into that instead of Horizon.
The core of the CFW shouldn't be firmware-specific at all -- it should generally support everything that it can.
I think they're pretty damn interchangeable.