The Vorwerk V100 XV model had a side brush absent on the Neato XV models, later added on the
Botvac. The firmware was shared and configured for the equipment with the unpublished USB command SetConfig, also used to specify lithium or NiMh battery type etc. where Vorwerk was first to use lithium batteries.
The same system board could have been used, even if not fully populated with components on the Neato -- no pictures of VR100 boards posted to compare (Vorwerk not sold in the U.S.). The firmware flashing procedure is a terminal emulator script including both memory flashing commands and configuration commands. The driver package installs a special terminal emulator "updater" program along with the driver. How the
Botvac was done is not published yet, and the new WiFi models can have a lot of differences, with updating over WiFi etc.
If the D5 runs Neato Control over USB, you should be able to turn on and off the side brush there. The posted command manual may omit the side brush commands but I think they are mentioned here somewhere, a tedious search. Will see if I can find it time permitting, I just seem to recall this being posted sometime maybe from Russia. Might confuse with the configuration commands, not sure. Maybe something like SetMotor SideBrush ON/OFF.
Incidentally side brushes do nothing on carpet where dirt is embedded and needs the main brush. I have never liked side brushes since having them on a Roomba. They break off against sharp edges, wear out easily, pull on electrical cords etc. One reason I got a Powerbot lacking them. Each to his own.
When I added a side brush to the original Neato XV, I powered a small gear motor off the vacuum power line with high capacity, as the load varies widely over different filter clogging states (so much the load serves as a proxy for air flow measurement).