This is a joint effort between Ford and Microsoft and it's about time they opened up the SDK to developers.
http://www.engadget.com/2009/12/18/ford-to-give-sync-some-app-store-flavor-opening-api-to-devs-in/
Will there be a .NET compatibile version of the SDK?
It sounds like you just have to be able to communicate via your application to it's API via bluetooth so the sky's the limit with developing apps on your iPhone, Android or even a bluetooth enabled Netbook.
Will this eventually be opened up to other automobile manufacturers or is Microsoft stuck to only licensing the Sync techology to the Ford platform?
If you have any inside information or details regarding this please post them. Maybe some of the devs from the article are SO readers and can provide some more details on the tech / api.