Erik Prince and similar have been trying to get that going again (for actual commercial cargo shipping related activities) for some time now.
It appears like they're trying to make an industry that works outside of conventional bounds. Just like with private military contractors. Not quite privateers like in the 1630s.
Except the constitution is clear that issuing letters of marque is reserved for congress, not the executive branch.
Also they have been prohibited by customary international law for over 150 years. The people talking about bringing them back are mostly trolling.
Lately there’s been quite a few things happening that are prohibited by customary international law.
I think the whole concept of international law may be on its last legs, frankly.