That's what we did with Konsole for KDE 4. KWin integrated compositing with a software fallback in case GL wasn't available, so there was simply no need to main

That's what we did with Konsole for KDE 4. KWin integrated compositing with a software fallback in case GL wasn't available, so there was simply no need to maintain the KDE 3.5-era fake transparency. Nowadays GNOME Shell simply requires a compositor, or so I thought, so it seems like you could assume one is present. The one issue is supporting the case of running gnome-terminal from non-GNOME environments that also don't have a compositor, but I think it would be fair to give up entirely on supporting that use case. However you might still want to handle the case of the compositor crashing (I think one of the dev's comments in this thread mentioned that), which is admittedly going to be annoying since it involves dealing with X.