This phase of the layout engine will add some key features and update/fix some previous issues.
Next generation tools like Maps and Lens utilize the concept of layers and Canvas should as well. This will help with finding/selecting elements, grouping, manipulating, etc...
Canvas would benefit from more explicit and fine-tuned controls for how users can layout the page.
I've taken a best-guess at performance work that is related to the layout engine.
Pinging @elastic/kibana-canvas (Team:Canvas)
Some suggested additions:
Design tools, such as Sketch, are a good reference point for how the UI could work:

Updated the issue to reflect @clintandrewhall's suggestions
++ @ryankeairns screenshot. We could have a greyed out lock that you just click when the element is highlight, and then in an accordion view be able to select multiple elements. Also, editing a single element in a group of selected or custom elements would be possible here.
Thanks @timductive, great collection!
These, on an initial look, don't seem directly related to the layout engine, ie. fixing or providing them don't appear to need (or solvable by) an aeroelastic code change, glad to discuss them one by one next week:
Maybe there are just varying definitions of the LE boundary, still it'd be useful to keep the placement and direct manipulation calculations (what I understand under LE - it's just calcs; no DOM involvement) separate from other UI affordances such as menus, context menus, DOM element capture, actual element insertion and update by React etc. (Having said this, it might make sense to have the concept of a "Layout UI" abstraction, because, if such drag&drop is needed elsewhere, it's nice to have a React component encapsulation for all the context menus, future layer/element manipulation side panels, keyboard shortcuts etc.- but currently, these things are not cleanly separated from unrelated menu, button etc. UI, not sure if @cqliu1 thinks it's even feasible to separate though)
For clarity, I'm adding a question mark in the original post, and also for these:
Hey @monfera thanks for taking a look. I agree, what I will do is edit this issue to clearly indicate things that are the Layout Engine and things that are Layout UI and then we can discuss what the right abstractions are. I'll also take a look and re-triage the issues that you mentioned.
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Design tools, such as Sketch, are a good reference point for how the UI could work: