Consumer and developers.
Which is what a proof of concept game would do.
Except that now you're building up a userbase for third party games instead of trying to steal their focus with such a limiting game (like WiiSports did).
Do you honestly believe that 3rd parties shit all over the Wii because it launched with Wii Sports? I assume you're referring to all of their excuses for why they couldn't succeed on the thing and why they were putting out putrid balls of trash on the thing... Is that right?
If you believe that, truly believe it, you're a bit gullible. That had nothing to do with why 3rd parties chose the releases they did; it was an excuse, a figment of imagination.
The only thing your suggestion does is that it splits the proof-of-concept into three separate games that people have to pay for rather than giving them one that does it just from buying the hardware.