I think the model should simply switch to household-based reporting only, regardless of status, especially if the joint set of taxpayers are claiming dependents

I think the model should simply switch to household-based reporting only, regardless of status, especially if the joint set of taxpayers are claiming dependents. Each reporting adult filer in the household would link to a household TIN (like a EIN) and it would be done in aggregate. The decision to file separately would be based on the dilution of deductions as number of filers increased, relative financial independence desired, or risk of incurring the tax liabilities of others in the household. (That would discourage roommates from filing jointly if they desired financial independence to avoid abusing the model)