I have very similar aims at using a very text and keyboard based set up which, like yourselves, I think can work with these devices. For it to be mobile as well would be great but given the hurdles I don't know how feasable that will be.
Clearly you both have slightly different aims and implementations. I've found both very interesting but obviously have my own biases.
To answer your original question, certainly the experience of others would seem to suggest that Onyx isn't likely to be very helpful:
https://www.mobileread.com/forums/sho...d.php?t=255084
There are those of us who have been trying to avoid this same situation arising with the Max and there certainly aren't any indications at this stage that it won't happen again.
I am likewise rather unimpressed by the range of keyboards supporting Bluetooth as I've said elsewhere:
https://www.mobileread.com/forums/sho...3&postcount=27
I suspect that delays associated with Bluetooth (allowing for pairing and stuff like that) are likely be swamped by the comparatively slow refresh rate of the eink screen. Though all the issues with the various firmwares are very concerning. I would have thought that this provides just more reasons for not relying on bluetooth.
I've pretty much given up on laptops since island keyboards became unavoidable. One can get good mechanical USB keyboards for the same price as Kwiz's BT one. I certainly don't want to be forced to use an island keyboard, even if I choose to use a tablet instead of a laptop because the latter have declined so far in quality. But perhaps this is all part of a general decline that means that USB keyboards won't even work in USB ports that are designed for them because companies like Onyx won't even support the USB ports on a device as expensive as the Max.
I like the idea of using BT to switching between devices. This is certainly an interesting way of getting around the unavoidable limitations of individual devices. Another possiblity is to use a bluetooth to USB hub. Some offer a somewhat similar functionality, although it is difficult to imagine these things being very convenient for mobile use and they also seem to have their quirks based on how they are implemented. That way one might both not have to buy yet another (it would seem to me, overpriced, sub-par quality) keyboard, and get to attach a decent keyboard to one's Boox cluster.
For example:
http://www.amazon.com/Aten-Technolog...er_top?ie=UTF8