Not sure I'm understanding what you're saying; so correct me if I'm wrong.

If you switch from WHM to RDM on CON you would still be the same level under this proposal. But SE could always just make you level it from whatever level the quest is (in my case its 20). One or the other has to be done.

I went over that in my third post in the OP.

You would in a sense be "enjoying RDM from 1" because the Advanced Class starts wherever the initial quest does.