Don’t see how this attracts new users to SN, something the team seem focused on currently. This opens up a lot of difficult UI challenges, with limited upside IMHO.
What happens when one founder fails to pay? Do the other founders get an extended window to pay? Does everyone have equal editing rights? How do you add someone else as an extra founder when the entire year has already been paid? Do they pay the existing founders? Do all founders get equal rewards in future too? How much extra content will be created because new territories can now have multiple founders?
Besides lowering the cost to creating territories, I am not sure what problem you are solving.
If you wish to reward people contributing in particular territories, it might just be better to see founders be able to send revenue splits to others for all posts in their territories and crowdfund the fees separately. Or as mentioned below, lower fees to setup sub-territories.