You have to dig through a lot of singing cats and poorly animated Sonic the Hedgehog parodies to find them, but YouTube does contain some hidden gems. Today's example is a home video of the 1992 Summer Consumer Electronic Show in Chicago, where Sega announced the SegaCD lineup... including Wing Commander and another never-released Origin port!
Origin balanced a complex, turbulent relationship between Sega, Nintendo and a number of outside licensors through the 'console wars' of the 1990s, which lead to a number of 'false starts' where games were announced but never released. The discovery here is that their deal with Sega to support the Sega CD also included a port of Ultima Underworld which never saw the light of day!
Like Wing Commander SegaCD, Ultima Underworld was likely ported by an outside developer and advertising would have been handled by Sega rather than Electronic Arts. As a result, the project has remained hidden for years, despite the public announcement seen in this video. A console port of the game was eventually released--for the original Playstation and only in Japan.
You can watch the whole video here. The SegaCD trailer starts at the 2m50s mark. The whole segment is a great look at 1990s trade shows (which seem here to feature Chester Cheeto instead of half-naked women)--and you can't help but feel some pride seeing the Wing Commander trailer appear first on the giant bank of TVs.