It would be just like a non-keeper, auction style fantasy league.

The owners were never going to agree to get rid of the reserve clause. A team keeps exclusive rights to a player until, what, he fulfills the rookie requirements, then the guy is an FA every year? That was never going to happen. And once that doesn't happen, clearly the players are not going to agree to something like 6 years of team control then best of luck.

The article says Miller was worried because how could he argue against "freedom." Easy ... freedom includes the right to enter a long-term contract. MLBPA should love earlier free agency but, in the FA merket ... what rational reason would a team have to negotiate a limit on how long it could sign a player for? You're the Yankees and 21-yo Mike Trout is a FA, you're gonna sign that guy for 10 years. Certainly the last 30-odd years of actual FA have shown us that teams prefer multi-year contracts where paymetns are spread out even when they don't expect production to be. If teams preferred contracts like 1/$50 and 2/$80 for Betts et al, that's what we'd see.

I don't know if the article mentions it but most obviously the trade market collapses. As hinted above, I don't have a clue how you develop young talent in this model, you certainly don't hand out big bonuses to draft picks. If we re-run the experiment, you either need college baseball to become a big thing or independent minor-leagues that can make real money. What happens to attendance if Ernie Banks, Reggie Jackson, Tony Gwynn, Derek Jeter are potentially changing teams every year?

And no way the owners want to re-run that history. In 1977 NL, the Reds, Dodgers and Phils all drew 2.5-3 M but no other team topped 1.5 M and two were under 1 M. In 2019 NL, the Marlins were under 1 M (amazingly) but even the Pirates made it to 1.49 M and the Dodgers nearly made it to 4 M, the Cards at 3.5 and the Rox to nearly 3 (them folks is crazy). They set revenue records nearly every year and they've seen franchise values go through the roof.

and the Rox to nearly 3 (them folks is crazy).

It's a nice place to get a beer and a burger and hang out with friends.

what rational reason would a team have to negotiate a limit on how long it could sign a player for?

NBA teams agreed on a max contract length. What it does is reduce the impact of the winner's curse. Whichever team wins the bidding for a free agent is the team that most overestimated his value. So they limit themselves to doing that for 4 or 5 years max instead of 10+.

MLBPA should love earlier free agency

They don't, because they like keeping younger players cost-controlled, for more money to be available for the veterans. The free agency threshold never gets reduced in any CBA because who that would serve to benefit are future players who are not yet union members and voters on that CBA. The 6 year threshold isn't some coincidence or historical artifact, it's because that's roughly the median years of service among union voters, such that there are as many or more players beyond it who have nothing to gain by reducing it.

Almost every union votes more pay to the more senior members this way - they have no reason to benefit incoming workers who aren't in the union yet.

The agents certainly want earlier free agency, and that's who you hear that from, not MLBPA.