List of performance issues that we would like to fix or investigate for 2.80:
* Transforming vertices in edit mode on high poly meshes is slow, due to overhead of depsgraph, mesh updates and and batch creation. Verify if there is anything unexpected happening here.
* BMesh to mesh conversion was happening all the time at some point, is this still the case? See check_rendered_viewport_visible, it now always happens when a 3D viewport is visible, and could be quite problematic for edit mode performance.
* Verify if custom data is only being preserved through modifier stack when needed (vertex colors, vertex groups, UVs)
* Manipulate modal callback performance may be problematic: T55458