Update - I located the problem. I'll post what I found here, just in case someone in the future is fruitlessly google searching for information.
First, the RCDLR (remote keyless door lock receiver) is located under the little storage tray in the passenger side rear, the flippy cover in the 3rd row seat area. You DO NOT have to remove the entire rear right interior panel to get to it. Just lift the rubber bottom out of the storage compartment, find the two or three screws that hold it in place, and carefully pull the compartment out. The RCDLR is clipped directly to the underside of that compartment.
What I found when I pulled my RCDLR out was the +12V pin in the plug was corroded completely off from the module. It is supposed to have 4 pins in the plug, three of which are used - red/white +12V, Black/white GND, and a green signal wire. I pulled my module out, turned the ignition to ON (probably not necessary), and confirmed I have 12V between the red/wht and blk/wht wires at the plug. Okay, so the wire harness is probably okay.
Next, I opened up the RCDLR module itself, pulled the pc board out of it, and sure enough I found one of the 4 pins broken off. That was supposed to be supplying 12v to the board. Also found some pretty significant corrosion all around the board. I cleaned it off as best I could, wire wheeled the broken contact pad, and soldered a piece of a small paperclip to take the place of the broken pin. OK now the pc board is going to see 12V.
I plugged the board back into the vehicle wire harness, checked on the back of the pins where they're soldered to the board, and confirmed 12v between the pins for red/wht and blk/wht. So my plug repair is working. Finally I turned the key on and scrolled through to the 'learn remote' section, and .... drum roll .... no change. Still no 'remote learning active' message. I plugged the tech2 into the vehicle and attempted to read information from the RCDLR module also, and still got 'no comm'.
So the problem is definitely my corrosion addled RCDLR module. Not the remotes, not the TPMS sensors, not a fuse, not the wiring harness, not programming. It's definitively this little 2 x 3 inch pc board. IDK whether I'm going to dive into figuring out how to flash a new module with the tech2 through tis2web or not. I may just live without the lack of keyless entry and the service TPMS message on the dash.
Just thought since I started the discussion I would close the loop.