See Inquirer Article, TSS thread and Core Developers site. (Love the logo, BTW.) It’s important to remember that this is the JBoss Group and not the code itself.
I have no idea what really went into this and I don't know enough to speculate. But it will be fascinating to see how this impacts the code -- it's entirely possible that JBoss The Project will be a stronger product for this. Having committers from multiple backgrounds and possibly competing interests can be a good thing. Of course, it's also possible marcf (or others) could have a cow and cutoff commit access for the CoreDev folks. That would be incredibly stupid (and marcf ain't stupid) -- JBoss has made a name by being one of the dynamic enterprise solutions, but most "enterprise" people won't put up with instability. And remember, it's all about the code.