Google's John Mueller said in a webmaster hangout yesterday at the 23:42 mark that they are adding the extended data to the API. He said:

The one thing that will be happening probably in the next couple of weeks or in a month or so is expanding the existence search analytics API.

So the existing API just to provide data from the longer timeframe that we have available now in search console.

So that's the one change that will definitely be happening.

There are no additional plans for other APIs at this moment, he added later but you can expect more data to come through the API in the upcoming weeks. I assume, Google will announce it when this is out or someone savvy will spot it when they are messing with the API.

John added:

With regards to other API is coming to Search Console API’s. That's something I I'm not aware of anything specific that we're going to announce at the moment. But if you do have recommendations for things that you definitely want to have in API’s then feel free to let us know maybe post in the the webmaster help forum or send us a tweet so that we can pass it on to the engineering team here.