SO I kinda decided to YOLO on my problem (set of songs, slowly growing, that are stuck in "Waiting" iCloud Status and inaccessible on any device but the Mac where I added them) and tried to subscribe to iTunes Match. My thinking was this: if iTunes Match is more open to music you have in the form of storing non-DRM copies, etc. Maybe there is some weird licensing issue with Apple Music for these songs that doesn't exist with iTunes Match. Logic is weak, I know, but, I had to try.
What happened then was the attached error. It wouldn't sign me up. That message seems pretty specific to be a generic response. Now I wonder if there isn't some genuinely broken thing causing my issue, and perhaps other issues, that is being worked out right now.
Because of this message, I'll wait a few days before quitting this experiment. Perhaps it really will be worked out. One thing is for sure, I had 43 songs "Waiting" and now I have 195. That's really obnoxious, but, it at least indicates that the library is "live" and being updated one way or another. If the problem is resolved, perhaps I'll wake up to 0 broken files in a day or so...
Fingers crossed, and, gonna go get a tattoo that says "Never Early Adopt, Ever Again" on my clicking finger