I'm not aware of any official investigations into this by the team, but here's my two cents:

* PS4 development requires purchase of an expensive development kit (2500$, although they sometimes lend them to developers for a year as well), which is probably just not financially viable for most contributors as there is no way to make back this money for them

* The PS4 SDK and everything related to it is under NDA and open sourcing code linking against it seems to be forbidden (e.g. the Unreal Engine excludes these parts from their public source code releases as well)

This is correct. There's a bunch of stuff that would require significant investment and also closed source components. It's telling when even Emby doesn't have a client in the PS4 store.