There was a question about using BLUETOOTH, but there is a problem – see below.
Bluetooth will have to come later. I need to check but certainly a few years ago it was expensive and difficult to implement.
The problem is that there needs to be interaction between the left and right units. For example when you hold the 2nd Fn key down on the left unit it enables alternative functions on the right side. These alternative functions include modifying cursor up to page up for example. Another alternative function is temproarily modifying space to back space. There are many others.

The left and right units transmit data to the dongle and the dongle can combine the functions described above.