I would start more with tweaks than wholesale changes -
- Fix the service time issue so that 6 years is the true maximum.
Just curious -- how you propose fixing the service time issue like this?
Not my post, but I would start with eliminating the concept of "days of service time" a player has to accumulate to get a year of service time.
Instead, if you are on the 26-man roster in a given season, it counts as a year, even if it was just one day. As a result players become free agents after they have played in six major league seasons (and not seven years minus three weeks). This would also prevent teams from keeping players in the minors at the beginning of their rookie season to gain an extra year.
If you wanted to soften this up a bit you could also allow for a larger threshold than one day, for example allowing a September callup that doesn't count as a year. If six years is too much that could also be reduced further. But in my opinion one of the biggest flaws of the current system is the possibility of teams gaining almost an entire seventh year on top when six should really be the maximum.
I don't know if free agency at a set age would be really viable because the timelines of prospects are so different. Take Brent Rooker for example. If there would really be (restricted) free agency at age 25 he would have been a free agent before even debuting.
Not directly related to that, but I would also change the rules for eligibility for the Rule 5 draft / the time when a player has to be added to the 40-man roster. It's just ridiculous that 16-year-old international prospects have only one year more than 21-year-old college players. Reduce the time for college players and give international players a bit more time, so they don't have to use up all their option years while still developing.
And after you have done that, maybe the number of option years could be reduced to prevent teams from keeping a player in the minors forever (and also delaying his eventual free agency).
Just a few ideas to make the system a bit fairer to players without weakening small- and mid-market teams too much...