I was a Gentoo user about 5 years ago. With Gentoo you can have both, if you only use stable packages you shouldn't broke your system. But if you are using bleeding edge packages thinks can break.
The problem with Vagabond is that it's not finished. I read Musashi after reading Vagabond because I didn't want to wait for the chapters anymore. Both are great and you should know there are mayor differences specially in Sasaki Kojirō character.
I hope they include the changes to the engine made for ET:QW. I'm particularly interested in megatexture. But they say "Doom3 source code" not Id tech 4, so they probably won't.
This says in limitations: "Android callable wrappers are needed any time the Android runtime needs to invoke managed code. Android callable wrappers are generated at compile time by the monodroid.exe tool, based on static analysis of IL. The net result of this: you cannot use dynamic languages (IronPython, IronRuby, etc.) in any scenario where subclassing of Java types is required (including indirect subclassing), as there's no way of extracting these dynamic types at compile time to generate the necessary Android callable wrappers."