Whenever possible, the user should be able to preview the effect of their ongoing interaction in other part of the UI.

For example:

• hovering a SV or container in the "Add SV/Container" modal should display it in the viewport and (temporarily) add it to the blueprint tree
• dragging a SV or container in the blueprint tree should display the effect of the candidate drop in the viewport and, potentially, the container selection panel children list
• dragging tiles in the viewport should display the effect in the blueprint tree and container section panel children list
• other?

To have that, we may need:

• some notion of "temporary" blueprints / tile tree
• a Preview/Commit enum added to relevant TreeActions
• maybe some visual language to signify that a given item is a temporary and the result of previewing the on-going user action

cc @jleibs