In the past (circa a few years ago) the connection between the main board for a display and the glass driver board would be a ribbon cable, LVDS signalling. Very straightforward and typically not soldered. There'd be a ribbon cable connector. So yeah, you could just put a board between easily. And there are LVDS to H264/H265 chips already.

But as the other comment points out, older HDCP is broken wide open so ... easier to just use that. Plenty HDCP strippers on the market.

HDMI 1.4 has been leaked and there are devices which will force communication to this protocol level.