Windows WDM drivers support up to 10 input and output channels per device, that's 5 stereo pairs in and out. So it's possible to have up to five output devices under windows, and five input devices, respectively.
For live streaming setups, having more distinct audio devices routable to mixer channels is key. As most audio sources used in live streaming cannot use ASIO (for examples, games and browsers seldom use ASIO drivers), more WDM channels are better.
I switched to the StudioLive III 32SC from a ********* UMC1820, where I had 5 adressable stereo output pairs going through the driver and interface, and then into an analog mixer – so it's definitely possible to have 10 channels, And I guess, the Studiolive Series has a far better digital architechture.
As the driver is already written to support multiple output channels, in my understanding, increasing the number of channels in the windows driver should not be more than the change of a constant, and maybe a bit more storage to store the assignments in Universal Control.