I've never seen CO offer a bump a at a remote station. Talk to the GA at EWR. Just because you have a boarding pass with seat assignment doesn't mean you won't be offered the bump. The GA's process bumps for domestic flights at the gate.

Your flight is showing Y0, so bumping is a possibility. This is a high-volume business traveler's flight based on the route and time of day, so expect people to have switched tickets to earlier/later flights. At the same time, if they do indeed need bumps, don't expect the DCA business types (they'll be wearing suits, you'll know) to get up and volunteer for a voucher, so I don't think it'll be that competitive.