Making a plugin that can retrieve CD info from an online database is somewhat trivial in itself.
I am not familiar with the cddb plugin though, is it integrated in the audio player & still functional? I know there is no service but is the plugin still in use, are calls to the plugin made even though there is no longer any data coming through? Or is the plugin deprecated & no longer used?
If it's still functional, according to the wiki, it only has one interface with 5 implemented functions, recreating the interface should not be very difficult in theory however those functions have not been documented so, as the service no longer works, we cannot test the functions to see what data they return to callers, there would be a need for some RE work to find out what those functions do & whether they are all needed.
And there is the issue of creating hooks to redirect the cddb calls as I am not sure the module can be replaced by a custom version like xai_plugin.
If hooks are needed, currently Cobra can patch modules when they get loaded but it doesn't support userland hooking, it's a feature I have been thinking about adding for some time so we would no longer be limited to module patching but could hook entire functions instead.
For now though, there is no such feature available.. It might be possible to make a custom module with our customised interface that Cobra would load whenever it detects that cddb gets loaded. Using the custom module offset in memory, Cobra could then patch cddb to redirect the function calls to the custom module function implementations & finally finish loading cddb into userland.
Something along those lines might work if ever the cddb module cannot be replaced directly, and if it can then it would just be a straightforward file swap.
In the end, when there is a will, there is a way..
But it's like you said, not enough active developers & not enough active development.
Because good will only goes so far, I also agree with you that incentives would help, and not just for homebrew development but also for R&D work such as reverse engineering & exploit writing. But for that, the scene would need to organise in a way it never has before & sadly, I am not too optimistic about that..