Yes I totally agree
just thought of it while writing. But there's also people here who store their library on external HDDs directly connected to the Ultra.
Just direct playback from a USB CD drive seemed like a cool and feasible idea. The hardware is there and should be capable enough. USB seems to be the preferred way to connect external DACs because the digital audio transfer is asynchronous. Playing a CD through USB vs optical possibly has the same benefits of reduced jitter and it's simply a nice and compact solution.