While I agree on said idea salary "negotiation" could still be used to ease the burdon on "long" rosters.
At the start of the season when new salaries are calculated you pay your top 5 players in ful. However you get 5% concuring discount on each of the next highest paid player to a maximum of 25% discount. So you get 5% on 6th man 10% on 7th 15% on 8th and so on. If you sell the player the new owner has to pay the full salary.