AFAIK, the only “plugins” available in Cubase’s Channel Strip are the ones built in. Most of us have substantial 3rd-party plugin libraries, e.g., UAD2, Waves, Plugin Alliance, etc. and it would be awesome to be able to use those in the Channel Strip instead of the built-ins. Luna does this, albeit with their own UAD plugs, but the point is that it’s extensible and changeable, e.g., Neve, SSL, API, etc.
Yes, I know I could create Panels and/or Quick Controls, but that’s quite labor intensive and not at all the same as having, say, the Neve 1073 look-and-feel.