Was there any more info released on the mysterious ship that was in CE's
terminal 6?
We really know nothing more about it, and it may never become important. Remember, the Librarian had over 100 (126 or something like that) "favored" intelligent species, so intelligence in the galaxy is likely to have much more than just the humans, covanant, flood, and forerunners.
I do want it to be explored though, if a civilization achieved space flight so much earlier than the covvies or humans after the halo ring firing, they could be pretty advanced and powerful indeed, maybe enough to stomp the two prior. Unless they reset themselves or wiped themselves out, or the flood ate them, etc.
My other theory is that the spacecraft was just in flight when the ring fired, and it simply shot through space for millennia until hitting the ring. That's a boring theory, and some people will refute it with the 7 life monitors shown in the terminal.
My strongest feeling is that it was just a way to show 343s solitude and longing for information, a bit of throwaway lore, really. But I do hope it's expored, as are other intelligent species in the galaxy. The Mantle of responsibility should cover more than just the Covanant races.