I believe there should not be renewal dates for teams. I believe if your purchase a team it should be for a season only. For the upcoming season, teams should be paid for before the allocation period begins.
This would create stronger leagues with committed owners. As an example, you go through the allocation period, trades, and then get all the way to March. Then a disgruntled owner bails because he is unhappy with the trades made up to this point. He can do this because his renewal date is not until some time in March. Now you have the problem of having to recruit a new owner just before the auction draft is to be held and the new season is to start.