A 10 year old PC carries 2.1 GiB/s (= 17 Gbps) over bog standard pipes without tuning or parallelism, as measured by "pv /dev/zero | cat > /dev/null". Uncompressed full HD is 1.5-3 Gbps. (Less actually, since codec output is going to be 4:2:2 or similar)

Yeah, you can come up with high bandwidth scenarios like stereo VR 144 Hz 4k HDR running on barely capable hardware. But 99% of users don't require such tricks and never see any upside from the performance-over-security compromise.

Even if you decide basic IPC is not fast enough, a shared memory buffer for raw frame data is reasonably secure too.