I have had a few developers ask if BlackBerry would be opening up more API access to BlackBerry Channels and it seems like it is in the works. Ofutur pointed out a thread to me on the BlackBerry Support Forums where BlackBerry employee MSohm has confirmed that you will be able to use the invoke framework to share text and images to channels you own. Devs can actually do that now with an invoke for sharing an image OR text but not both together yet.
In short what we are seeing of BlackBerry Channels is just the beginning and BlackBerry has much more planned on that front. Let us know what sort of API access you want BlackBerry to add in the future!