There's a virtuous cycle thing going on here: Someone releases a product with hackable/open specs (Xiaomi has a good track record here), people are overjoyed because you can't easily get good hardware for cheap and build a bunch of software around it, thus (usually greatly) extending the capabilities of the product, other people buy that product because it's much more advanced than competitors (because of all the ext…
On the other hand, they also open themselves to people just making their own versions of the product for much less. If you choose them for their hackability, your core processors will probably have minimal development boards available for less than $2.50 each if you're using anything less powerful than a Cortex-M4 ARM core. And now you have a huge part of your value proposition - the easy-to-use and user-configurable…
There is a large exception for anything with a camera. Everything to do with the chipsets or sensors is under NDA and inaccessible unless you want to produce thousands of devices. I would love to be able to play with (say) a half-decent 2 year old camera chipset+sensor, which would apparently cost just a few $, but it's a no go.
For instance, the Raspberry Pi camera is entirely handled by closed-source blobs on the CPU and GPU. The best you can do is get cheap USB webcams from China for $20-30, but they're power hungry and you can't run them from a microcontroller.