Microsoft has made their plans for extending Cortana a little clearer. Although it was already announced a while back that skill development would be supported, not much was stated. This past week and the company's Windows 10 Creators Developer conference more light was brought to Cortana Skill Development.
You can learn more by watching the presentaiton on "Improving engagement with Windows and Cortana Skills". If you are only interested in Cortana Skill development, move forward to the point about 20 minutes in. The presentation is only 11:43 minutes long, And the final demo does not work, but you get a very clear picture of how similar this is. There is a portal where you enter your intent schema along with creating sample utterances.
The entire project is based on another artifiical intelligence project Microsoft has had going: LUIS, the Language Understanding Intelligent Service. This is a natural language understanding web service that you can pass speech into and when you have set it up with an Intent Schema and sample utterances, LUIS will return to your code the intent found in that speech. This seems intended to be used for your own ChatBot, and is also simliar to Amazon Lex service available through AWS. LUIS is currently in beta and there is no charge to use it.
More information is at: https://dev.microsoft.com/cortana. The program is still in limited beta, so folks on the outside still can't get at the developer portal to register skills. It seems as if Feb 27 is the big day in which we will be able to get our own hands on these tools and try them out for ourselves.