It would require a 1040X because a conversion must be reported on Form 8606. Because the distribution was in 2019, a rollover however late would also be reported on the 2019 return.
Note that even if this provision passes into law, like some other CARES Act provisions, retirement plans are NOT REQUIRED to adopt these provisions. And it’s possible that some plan custodians will take their time to decide should the provision pass. For custodians, 2019 roll backs are even more disruptive to their processing platforms than the 2020 RMD waiver.
Presumably, if VG accepts 2019 RMD rollovers, they would report them like an ordinary 60 day rollover conversion made in December and rolled into the Roth in January. Form 5498 would show a 2020 conversion for purposes of the conversion 5 year holding period, but the conversion would be reported by the taxpayer on a 2019 or 2019 amended return using Form 8606. The IRS might also add additional reporting changes. Note that these are not 3 year repayments like CRDs, rather they must be completed by 11/30/2020 and the taxes paid with the 2019 return.
Note that you would leave your 2019 QCD as is, but since 2019 RMDs would be waived the QCD saves you less. However, if you did the QCD out of order, it no longer matters since with no 2019 RMDs, a QCD could be done anytime in relation to other distributions.
If this provision becomes law, it will take VG some time to decide how to deal with rollovers, whether to accept them, and how to process them.