1. Image Editor 2. Tilemaps 3. Non uniform spritesheets(Frames of different sizes). That is, compressed spritesheets. Even more: Don't cut spritesheets into separate images. It's a good practice in opengl / direct3d domain but it applies to htm5 too i think.
All the bits you listed sound great. "Hotspot & image points for sprites Collision polygons Good support for tilemaps Families"
And maybe a few small convenience tools. 1. Duplicate layout "includes objects and layers" 2.create prefab out of selected. "mostly due to not having tilemaps but would still be useful" 3. Visible grid, to match snap to grid feature.