Given the hazard of jointandseveralliabilityand the fact that filing jointly is an irrevocable election, I really think the default assumption should be separate filing.
Indeed, the Australian government said last year that it would replace the principle of jointandseveralliability for auditors with that of proportionate liability, and also allow auditors to incorporate.
Jointandseveralliability means that each spouse is liable for up to the full amount of the liability, though the IRS cannot collect more than the full amount of the liability.
The jointandseveralliability cannot be undone, except through an innocent spouse proceeding, which we know from this and many other cases is anything but a piece of cake for the taxpayer.
According to the Gibson update, not only does the Amnesty program release cooperating applicants from potential criminal liability, it prevents civil plaintiffs from recovering treble damages and protects civil defendants from jointandseveralliability.