For the message pictures, I'm planning to just use the regular event "show picture" function. So you can display however many pictures you want and control where and how they appear/disappear, whether they're highlighted or darkened, etc.
Which is already possible even without any plugins. Take a look at this vine:
https://vine.co/v/imjadPIxlbP
It's a lot of work though to maintain.
Ideally there should be an easier way to manage the visuals, but it shouldn't be completely up to the plugin to handle it.
One idea was to set the "active" picture that's currently "speaking".
So you might say "active" pictures have normal tinting, while "inactive" pictures have darker tints.
You would then use plugin commands in your event to designate who is currently "speaking", and the game would handle what happens afterwards, like perhaps animated faces for the speaker.
And for any other functionality that the plugin doesn't cover, you would just use regular events.