I would expect to have digital playback devices (USB, CD, digital player) going IN to a DAC.
Rather than re-creating another CD player that can connect to a BDP (which requires a whole new design), I'd rather see a BDP with an integrated CD drive, if it can be done without compromising the sound quality.
If the power supply and CD noise isn't an issue, all that should be required is a chassis. A CD drive should be able to connect to a BDP as a USB device (already the default input on a BDP) or one of the internal SATA connectors.