Overall I like the idea and the proposed plan!
This makes sense as, to move faster at a higher level, the lower levels need to have less disruptive changes. Would this LTS be specifically for AI Developer Desktop or would it be an option for traditional and atomic desktops too? What I worry about is the maintenance factor on backports or testing. The wider the net the more help, but also the greater the surface area and want/need for changes for use cases.