Even if you are forced to cooperate for 5 editions it is still a loophole to skip the waiting list, just that that loophole takes 5 editions longer. And then when that period is over it will become messy, for example if both jurors want to stay and go to seperate countries etc. This will get confusing and frustrating.
There are two cases we have to look at
Regular x Regular co jury
This is totally fine, it should be allowed. No one will lose their spot, instead we will look at it as if one of the regular members takes a "break", so for the time the co jury exists someone from the waiting list can send an entry as well.
Regular x non regular co jury
This is the problematic one. I think Uto made a very good point, all the rights should be held by the original contestant. Therefore the only solution I see is that the non regular member will have to stay in the co jury with the regular member for their entire time in the contest. If the regular member leaves/switches/break whatever, then the non regular one has to as well. If two members truly care about co jurying then this rule shouldn't be a problem.