People who don't have credit? I used a debit card at one point, though I don't anymore.
But also, they're looking at moving their credit cards to Discover as well, which would make huge waves (both in the credit card/banking world, and for their customers, who would probably find it very annoying).
I’d just drop them.
I suspect the play they're making is that putting millions of new Discover cards out there will be a tipping point, pressuring the remaining merchants who don't take it, as a play to break the Visa/MC duopoly.
This could be not that hard to pull off. American Express historically was less accepted because of their high fees, but I don't think Discover has or had that problem.