First off thanks for the work you two have been doing on this, this is amazing, and makes my work infinitely easier!

One minor thing I'd add is designating an end frame, say I want to have an emitter start after a certain emitter has stopped, for example an explosing followed by a smoke trail.

The bigger ask is working in a timeline somehow, so you are able to key in certain values, and lerp between the keys.  I'm imagining this would be quite an overhaul, though maybe there are similar simpler solutions to what I'm imagining.  

I'm imagining little key buttons next to each property, that'd add the key to the timeline.  Perhaps the timeline has a track for each property, or the user can add a track for the properties that they need.  Like photoshop's timeline, you can have emitters take up a certain amount of frames, every frame meaning they are emitting particles.  Underneath that are the properties, with their respective keys.