If you have a system whereby all FIs have to hold professional licences you will have an instructor body top-heavy with hours builders. They are not necessarily (careful use of word!) the best teacher material.
Let's have PPL + Suitable Experience + Entry Assessment + FI Course = some sort of (N)CPL(Restricted to FI privileges) / FI (R) with a similar upgrade path from (R) to full FI as currently exists.