FWIW, I don't care if the screen briefly flickers during switching.

You just need to strip the hdcp on the source.

It still seems the right hardware, upstream or downstream depending on which direction you're viewing things from, could keep the connection alive with the HDID pre-negotiated. Like, assume the hardware doesn't change between switching. If you're the TV's firmware and have the CPU power to, why renegotiate when switching inputs. Solve for the default case and have it standing by and running hot. it's not like the panel is going to change in the interim.