My reasoning is that implementers shouldn't have to know that it is implemented as a modal (and therefore mark it up as such). The previous approach was a very basic decorator pattern that just required the magic class name to create a plug-in (plus data/settings for any overrides.
Session timeout is also on of the ones that I'm not sure I'd even use with an element selector event. It isn't really a dynamic plug-in, it could just be set in whatever the successor is to `setting.js`.