We fully intend to make the APIs public, but are working with existing partners to implement. We are trying to be flexible and understanding, also are not throwing legal threats :)
What I'm hearing is you want partners to trust your intents but you don't trust any of theirs—as evidenced by the terms of service that is required and binding. The "not throwing legal threats" part comes off very hollow in that context.
If you did trust your partners, you'd make a new API alongside the current setup, and it would be so awesome that people would switch on their own. But as others already pointed out, it seems the value in the new API is self-serving and is inexistent for your partners.
I'm all for collaboration but I suspect you are trying to build a moat around your business and make a ubiquitous platform. I sincerely hope this backfires.
First we strong arm current implementations, forcing them into a Private API that we 'intend' to make public. Sort of how we intend to go to the gym, intend to drink less and intend to think about how our actions affect others in order to be better people this year.
Wait. Why would we believe this statement? Why would the people who willingly implement your private API care about it going public?
This "intend" is as much worth as the intent to build a comprehensive test suite and intent to document the code later.