As for event-written plugins/behaviors - these are actually quite a popular and oft-requested feature.
For ass-hats like me who can't program to save, well... anything's life...
This would be a very welcome and powerful addition to Construct.
I have spent countless HOURS even DAYS making some custom thingy-ma-bob do a hers-a-whatsit for the thingy-mer-jig, only to want to use it again somewhere else on another project. It would be sweet as to be able somehow export the event group/selection/sheet/whatever to make a single-click implemented "plugin" that could be used by anyone and everyone.
As much as an online multiplayer plugin makes me gush... I would LOVE to see something like this (especially if anyone has a chnace in hell of keeping up with lucid ).