I had one other thought on expanding....for mine, I've decided to go with this so far:

Each of the 20 existing teams can protect 15 players.   Each of the 4 new teams then takes turns picking from the unprotected players;  35 rounds.  After each existing team has lost 7 players, they are then ineligible to lose any more.   At the end of this, each existing team (they start with 40) will be down to 33 players, and each new team will have 35. 

Running through a mock draft to see how it works, the 4 new teams will still *really* suck...which may be ok, but it led me to have a wild-hair idea...what if, to balance things out more....drop one of the "regular" rounds and add one more round at the end, where NO players were allowed to be protected...so essentially each of the 4 new teams would get the best player from 5 of the existing teams.  Think that'd be TOO radical, too harsh?  Would it make the expansion teams TOO good?