For possible fall release... I think having a trade deadline earlier in the season would be beneficial for a few reasons. I will use Days 55 as an example (which falls around Game 50).
Also to go along with this suggestion, I would also recommend that those players who are "happy with their current contract", be open to re-negotiating or flat our refusing to re-sign around Day 45 (around Game 40).
1) First, I think it would add some excitement to the game mid-season, giving managers another milestone to look forward to. Preparing for the draft is exciting. Silly season/free agency is exciting. The playoff race toward the end of season is exciting + actual playoffs. Why not add something in the middle for managers to look forward to?
Around Day 45, players are either willing to re-sign with your team or refuse to re-sign. You then have 10 days to get your trades in before Day 55. Personally, I think it would be an exciting 10 days of managers trying to wheel and deal before the deadline hits. Then all managers must live with their decisions for the remaining 10 regular season games and through the playoffs.
2) Second, it would require managers to be proactive and take calculated risks based on their expected finish. It would eliminate teams from making those final day trades to stack their teams for relegation - and would also not allow managers to trade expiring contracts on the final day of the season, which caused an issue this past season.
3) Finally, this is how professional sports are run - and I know that as a fan, I get really excited around the trade deadline every year in anticipation of what trades will be made.