I get and like the idea of gradually increasing the security/complexity over time.

However what I find misleading/problematic is to suggest switching from mobile (=hot) wallet to cold storage (switching to a Jade) using _the same seed_ (or did I misunderstand how that part works?)

This suggests you can retroactively increase the security of the seed which is against best practices.

When switching from hot to cold storage you should support creating a new seed on the Jade and then sweep the funds.