This is not going to result in any sizeable increase in tax revenue from 1099ks for sales for the IRS. It is just going to be more reporting, but most sellers will claim a cost basis for their items they have sold. The IRS is not going to be out there auditing 1099ks under 20k.
The real thing they are trying to catch is 1099k income from gig jobs (uber, grubhub, airbnb, etc). These companies moved away from 1099misc ($600 threshold) and switched to issuing 1099ks (200/20k threshold). So you end up with a big chunk of unreported income and the bigger $$$$ unreported Self employment tax. If played right, someone could have 3 or 4 gig jobs netting 40k without any of it being reported and not paying taxes.