Some notes on your notes. SCART can also transmit 480p as I mentioned above. That plus the ease of configuration on the OSSC side is the main reason I recommend it.
Regarding RF output, the NES still had an external box thing, but it also had a modulator internally. Not really sure why it had both, but it did… PCE/TG16 also had internal modulators. But even as recent as the original Xbox had options for getting RF if you really wanted it.
Regarding region lock, I know that you can play JP games on a US console by way of a boot disc. Not sure about PAL and NTSC, though.