Regarding the libaacs solution, in fact, it was someone on a Slysoft thread who told me how to download and where to install those and something else in Windows 10 to enable VLC player to play BDs-and it worked! I could play almost any 1080p BD in my collection. However, somehow it stopped working a week or so later and I didn't write down the steps to reset and/or repeat the installs, and didn't have time to get back to that guy on the thread. But that proves that a similar solution is very applicable to JRiver.
Alternately, MC could pursue a different scheme to achieve the same. And they should since there's 1080p BD is no longer the gold standard, and besides the request is for playing BDs, not ripping them.
I'd post my request at Doom9 if you think it would help expedite creation of some kind of JRiver plug-in, BUT I am NO kind of coder, and don't care to be. I just want to install the software and thereafter have it work its BD playing magic on JRiver.