The only amazing thing is that front offices didn't get better at this form of evaluation and projection, a long time sooner. Plouffe summed it up: "I wasn't good enough [anymore]." No getting around that. Anymore.
IMO the players association needs to face this reality and take the lead on working toward a salary system that leaves the players feeling less used or disappointed when they hit their 30s, particularly college players who reach the majors at an older age. Players need to get paid when they still are good enough. The plan should be independent of the separate issue of what percent of revenues should go to the players overall.
The clubs have been adamant about the system leaving some way for the smaller-market clubs to hang on to their good players, and to a lesser extent avoid all the good players flocking to "desirable" cities only.
The players quite reasonably don't want to find out how much they earn only after playing the season and seeing what numbers they put up. A system built solely on performance incentives won't fly.
Sometimes players want to move to a different team, but I have to believe most free agents move only because they have to do it in order to follow the money. Conversely, sometimes a team is happy to see a troublesome player move on, but usually they reluctantly say goodbye because price/performance has become the only problem.
Would Torii Hunter have left the Twins if he could have gotten the same money from them? Would Eddie Rosario be gone if Alex Kirilloff was destined to get the same money as him if the projections turn out to be true? Neither of these guys was troublesome and neither guy disliked his team.
Yet teams and players shouldn't have to be tied to each other. How do you move on, with minimal hard feelings, when you lack the fig leaf that "salary differences" provide?
I'd love to see some intelligent alternatives to the present salary system put forward here, that don't ignore the concerns I listed (and maybe some additional realities I forgot).