Consider using libgranite for a more polished UI
I'm not sure whether this would be applicable to Diodon'c core UI, but I have encountered a number of third-party plugins that would certainly benefit from a more polished UI toolkit such as provided for by Elementary OS' libgranite¹. I filed this suggestion as a request/bug² with the developer of the plugin Sticky, suggesting that Granite's decorated windows³ would be perfect for Sticky. Whilst he was receptive to the idea, he rightly raised the issue of bringing in a dependency.
As I say, I don't know whether Granite could ever be of any use to Diodon's core UI, and I certainly wouldn't countenance bringing in unneccessary dependencies. However, if Granite could be of some use to Diodon I would humbly suggest that the core developers adopt it. It would provide a powerful and rather beautiful UI toolkid for plugin developers who are reluctant (perhaps rightly so) to bring in additional dependencies themselves (if you forgive the turn of phrase).
Sorry for the late response - I haven't figure out yet how to get notified when new blueprints are added - do not think that it is actually possible
At this point there is only one signal dialog in Diodon which is the preferences dialog. This will be replaced soon as Bug #1235830 So I think it doesn't make much sense to include libgranite as a dependency in Diodon core.
I do welcome plugins though to include more dependencies if it makes sense to their usage - e.g. if some wants to write a plugin which integrates well into elemantry OS.
I would also consider those plugins to be included to Diodon core plugins as long as it adds new value to Diodon and is written well. If the plugin adds new dependencies it can always be included in a separate package to not affect any other users who then have to install for them unnecessary plugins.
Hope this clarifies. Closing this blueprint therefore but let me know if there are questions.