New business model?
VT should write their own AV scanner and pay the AV engines that actually first detect a given piece of malware a royalty - like Spotify does with artists.
Then you'd have a proper competition to see who can write the best detection software.
Best of all, that allows VT to keep the API open to subscribers who can write whatever they want - next gen detection, or another "value-add" (read that as: search toolbar)... only they would also have to pay that royalty to the AV engines that get first detection. If you don't contribute, that's fine - because you're paying the contributors for their hard work. Conversely, if you believe you're better than the rest, you can still share your results with VT and cash out as always the first one to detect. 1337!
You could probably even anonymise the source detector with BitCoin. Even VT doesn't know who it was who first detected, just that they did and that there's a wallet that needs to be paid.
If artists can't sell CDs anymore, why should AV vendors sell endpoint software?