My understanding is these serve no purpose whatsoever any more. Then wouldn’t monitors have a mode in their EDID which minimizes bandwidth requirements by dropping the blankings to 1 (or 0)?
As an example, if you have a non-Thunderbolt USB C dock with USB 3.0 and two video outputs then you can squeeze a 2560x1440@60Hz and a 1920x1080@60Hz in the available bandwidth just by changing the V Blank to 6 for both, the CVT standards prescribe 41 and 31 respectively and then they won’t fit. 12 euros to dollars
the resolutions available depend on more than the USB-C dock
grafics hardware has influence as well
if the dock has none it depends highly on the system and if the USB-C ports are fed with a DisplayPort signal
and don’t forget the EDID data
this handles the connection specification and is optimised for both sides of the connection to work
if not, the display shows no useful picture or black