I like this but there is one change I would make

Only have 15 rounds of expansion with 4 teams - that means 60 players
Each current team would lose only 3 players each: 20 teams x 3 players
A full roster is 17 players (inc 2 goalies) plus prospects
the expansion teams would still have to go to FA or the draft to flesh out their rosters rather than be gifted a fully active team of players plus prospects