Found a device to strip HDCP 2.2, to fix home theatre compatibility issues.
So I bought one. I now have a Panasonic DMP-UB400. It has good 4K HDR to SDR conversion, with an adjustment slider, and it outputs 1080p with no HDCP issues on my setup, which includes a Marantz SR5010 4K-compatible receiver and a Sony VPL-HW45ES 1080p projector.
Unfortunately, as expected the projector does not support HDCP 2.2. For 4K movies downsampled to 1080p, that's actually not a problem, because the Panasonic Blu-ray player will happily handshake at HDCP 1.4 for 1080p. The weird quirk though is Netflix won't work at all. Even if you manually force 1080p output in the player settings the Netflix app refuses to even launch if it doesn't detect HDCP 2.2.
So I bought this:
Revesun HDMI Splitter 1 in 2 out
It's just a splitter, but one with an interesting feature. It will handshake an HDCP 2.2 link with the player, but then strip the signal of HDCP 2.2, and output the video as 1080p. With this little guy in the chain, the player sees HDCP 2.2, but the projector does not need it, and everyone's happy.
The other scenario where I could see this helping is with my Bell Fibe TV PVR. The PVR they usually spec these days for home installs is their 4K PVR. However, with my Denon 4K receiver and 768p plasma, the PVR refuses to connect. It will display something on the TV, but that something is just a message saying I need HDCP 2.2 for it to work. So what I have to do with that TV is bypass the receiver and connect the 4K PVR directly to the TV. I have to run sound separately to the receiver. It's clear there is some issue with 4K device compatibility with some older equipment, even when just transmitting 1080p (which shouldn't need HDCP 2.2.) I haven't tried it yet, but I'm thinking putting the Revesun HDMI splitter in the chain would eliminate this problem too.
I originally wrote that it changes HDCP 2.2 to 1.4 for the display, but that may be incorrect. According to other posters, HDCP is stripped completely. No replacement with HDCP 1.4.