You're assuming that IRS is not going to automatically allow the higher exclusion for MFJ returns from community-property states?  That's probably a safe assumption, but I would wait a few weeks to see if they announce something about this.  

There are two categories of returns involved:  Those filed before the exclusion was enacted; and those filed with the exclusion allowed to only one spouse.  (I wouldn't charge a fee for doing those, preparers should know better.)  The first category, the logical action would be for IRS to ask the taxpayers if it is community income. They can't always know  just from the address.  Don't expect that from IRS, though. The second category, they could do the same, but they're very busy with other problems.

I gave my clients an envelope addressed to IRS with a tracking-number label, and I printed the tracking history that showed delivery.  If MFJ-to-MFS returns can now be e-filed, what kind of ack is received?  Enough to withstand IRS claim of late filing?