A things here to keep in mind
1) in the pre-CYMS system, school "B" that had you on a WL and were going to offer you an acceptance was required to contact school "A" where you already held an acceptance. The reason being again for enrollment planning and not having an empty seat. That is in the culture of medical school admissions so I am sure much that still goes on
2) On a PTE, your acceptance school knows that you may be on a WL. Indeed it is assumed that if you remain on a WL, you would take that new school over the one where you hold acceptance.
3) The underlying data/system between AMCAS, the processing company and the schools certainly has the info on a student. I am sure there is a way that the "front end" at the schools can be configured so reports on PTE and CTE students will be flagged when they have a new acceptance. As an admissions officer I would certainly want to know this as when a PTE gets a new acceptance, it would be assumed they will go there. Else, why would you have remained on a WL. Now whether the front end actually gets this configuration, if reports are set to run this, If schools actually do this, I dont know. If I were to do it, I would set a 5 day flag on it. That is, if PTE student X gets a new acceptance on the report, 5 days latter I would generate an email inquiring reminding them to withdraw or change their PTE. After two weeks another letter. Then final letter.
4) since each school now sets its own policy, I would suggest PTE students who get a WL acceptance, send an email to both schools quoting the AAMC guidelines on how long you should be allowed to decide
5) However, I also think that every student should have their WL schools "ranked" and should know immediately to take the acceptance or not. You remained on the WL so presumably that is where you want to go.
Everything you are saying makes all the sense in the world, so I totally see why you think this. I, on the other hand, am unburdened by being an admissions professional who spent many years operating under the old system. AAMC took away the MAR and revamped the entire system for a reason. All of the assumptions you are making with respect to how reports can be configured would undermine these changes.
I get that in the old days, school B would reach out to school A, and that it was in all the schools' interest to do so. It was not so much in the students' interest. AAMC took away school B's ability to know who school A is, so they can't contact them. THIS IS NOT AN ACCIDENT; IT'S BY DESIGN!!!! In the new world, why would AAMC take this away, but give PTE schools the ability to configure a report and get it anyway (minus the name of the specific school)?
Of course you would want all of this information as an admission officer. The fact is that AAMC, out of fear of potential antitrust litigation, took it away from you because it only served your interests and inhibited candidates' ability to benefit from competition between schools, especially after 4/30. Schools are now free to compete on price, and poach to their heart's content. The only limit on this is a school's ability to require, as a condition of keeping an A, that a candidate select PTE/CTE by a certain date. All schools at which a candidate holds an A or a WL can see PTE/CTE after 4/30, and they can either allow the student to keep the A or WL, or they can rescind it. The PTE/CTE school cannot see the other As or WLs because allowing them to do so would give back to them some of the ability to act anticompetitively that AAMC just took away.
To quote you -- schools do not have to give a candidate price transparency before requiring them to make a decision. Maybe they wouldn't want to allow candidates to have the necessary time to receive a FA offer from another school after 4/30 either. Tough -- that's why they can't see the other A or WL, and don't get a vote anymore. Honestly, you are only thinking about this from the schools' point of view, and are failing to take into account that the tools made available to schools in managing this process changed for a reason.
Schools have all the leverage until applicants receive multiple As, at which point it changes. Schools previously used the MAR to limit this leverage, and AAMC thought this might create legal issues down the road, so they took it away, along with all the other goodies schools could use to manage their yield and limit the amount of price competition between the schools. The advice you give regarding telling a PTE about a new A (apparently, if candidates don't do so, they risk jeopardizing their A through some unpublicized ability the schools have to mine AAMC acceptance and WL data), and maybe seeking their permission to keep the A for whatever extended period the new school might allow someone to keep it only serves to undermine the new power the AAMC has graciously decided to grant applicants.
By the way, in this brave new world, some people might want to stay on WLs not because they prefer them over their PTE school, but because they want to see if an A from a WL might turn into a money offer that could be used to get money from the PTE school. Or maybe money would turn the WL school into a first choice. You never know if you don't let it play out.