All of the official versions since the one you mentioned also support AOSP Pie decryption. So, if that's all that was needed to support decryption on stock Pie, it would already be working. The point is, it isn't. I think @JEANRIVERA has worked with @Captain_Throwback in the past, so I'm sure he's speaking on behalf of him when he says that it may never work. I'm not sure how you would ever expect to get a response from Captain_Throwback directly since he doesn't post here anymore.
P.S. @scottnet you could join the TWRP Testing Slack and ask him directly, and then let us know what he says...