I can safely say that there won't be an API for Phalcon as you described it. As @doit76 mentioned, one can do such a task through PHP's API.
However there are a couple of solutions to the issue you are presenting.
a) You can always work on helping Phalcon with added functionality and/or bug fixes. A simple pull request in the cphalcon github repo will be enough
b) You can create addons that would be loaded as modules on the server (like Phalcon is) requiring Phalcon to be loaded - a bit tricky here
c) You can create PHP code that complements Phalcon and submit it in the incubator repository so that others can take advantage of this functionality
There are times that the incubator serves as a source for new functionality - we have done that in the past.
Any submissions or help are welcome. Your suggestion unfortunately introduces the endless dependency problem i.e. I have component A that you can load on your browser but in order to use it you will need component B or C etc. This is a path we do not want to go since it will increase the complexity of Phalcon in terms of setting up.