If you think about it a bit longer I think you will see that it will be not a lot of UBs or it will depend.
I think we need to specify the DG picking a bit more, pacov has corrected it but now some things are not clarified. So both teams are in the lobby, from the schedule it is clear who is on light and who on dark.
Step1: both teams declare which player on the other team will be forced to play a DG of their choice. I dont think it is really important who declares that first but I am 100% sure there will be someone who thinks its important so we should also determine which side has to declare the forced player first.
Step2: Dark now has the option to either tell light which DG they have to play or let the other player on light pick his free DG first.
Step3: Light would (in theory) have the choice to either tell the free player on Dark to make his pick and then tell the forced player his DG or tell the forced player first and then let the other player pick. I think no one will tell the forced DG first as it would give more options to the free to pick player.
Step4: Depending on Step2 Dark either has a free choice now or will hear from light which DG the player will play.
Now my point against the UB. I think in most cases you will have to pick your DG first and then hear what the teammate will play. It has some advantages to have at least one general on your team. As most probably the forced DG will not be a general, I think the free choice will be a general in most games. But it could also come different.
Pacov I think you should take these four steps and post them somewhere official so there is no discussion in game lobbies about it. You will have to rephrase them ofc.