Of the apps you listed, only Tomboy is an official Gnome app. The others are just third-party apps written using the gnome libs and Mono. Furthermore, there are (in my opinion) better gtk or gnome apps in each category that that don't use Mono. I don't see how this makes Mono "firmly entrenched" in Gnome.
For the record, I am a long time user of gnome, but am deeply skeptical about Mono, and avoid it like the plague. This attitude seems to be fairly common in the gnome community in my experience.
Also, to keep this message on topic, I don't use QT or even have it installed on my systems, but I think this license change is a smart idea, and I hope it increases QT usage in areas where it makes sense.