If not accommodated at launch, I’m sure HDMI 240/288p is possible to implement.
I googled the Wii2HDMI and PS2toHDMI adapters, in the case of Wii that one seems to already upscale to 720 or 1080p. PS2toHDMI seems to pass through 480i/480p, but unclear what it does with 240p if playing PS1 games on PS2. In both cases, it seems the adapters take the component video as input, so I’d think this is a moot point because it would be better to just pipe the component directly into the OSSC Pro.
Regarding HDCP stripping, I have no idea.