like others said, it doesn't do the video processing itself, which is why they are able to make the battery life so long and the size of the device so small. and that's why it doesn't need or can't have an hdmi port. it makes perfect sense to offload that to another device that most everyone already has.
what does "raw data for use with opengl" mean? the integration into unity should provide the ability to implement rather extensive video sequencing ideas. there are a few people i follow on twitter that i have seen do rather complicated stuff, and that's because unity is rather nice.
i am just curious what your use cases are to want these extra features that you can't already do with the instrument, and what that has to do with it being a "proprietary" device.
and if you want an open source “portable keyboard thing”, then there’s already the organelle. it is no surprise it isn’t much cheaper and isn’t as well designed, for both hardware and software.
https://www.critterandguitari.com/organelle