> a k/b with an extra battery for weight/balance, and actual friction hinges to hold the tablet at the desired angle.

which doesn't exist. You can't just design half of a device and tell customers that 3rd parties will come up with the rest... in time.

Just a not fully considered thought, but maybe we could 3D-print hinges for this product?

Or, BT keyboards with trackpads (they do not consume much power) including hinges could be in commerce.

there are products like that but all of them (that I known) are designed for specific devices, either a Surface or an iPad (Brydge, Doqo)

Let me know if you find something on the market that may work with this specific tablet.