My reading of the policy proposal is that it aims to allow people who received allocations under the legacy allocation scheme to expand their address space in a contiguous fashion without having to shift out of their existing address space.

Maybe I'm being dense but how are the restricted from doing this under the current policy framework?

They can extend up to a /29 today if they have the need. If they need more then they get two block or renumber. Thats the current framework, this policy doesn't really change that as far as I can tell.