Mark agrees making a GUI you can use to set up the persistence time, UI modifications over a basic structure, font size/style, but that's it.
Here's what Mark Shuttleworth says about 'stacking' (make the bubbles dock downwards as they are initiated and start to stack up as the bubble times finish away) or a close button on NotifyOSD:
Please, no. I would urge Mirco NOT to take patches that introduce that sort of behaviour. We are trying to build clean and tested codebases, and the more alternative pathways we support, the less maintainable it becomes.
The design experience of Notify-OSD is what it is. Changing the style is one thing, changing the behaviour of the bubbles is another thing entirely. We are just NOT going to support simultaneous display, the design is queued and serialized.