It would be cool if Rhino could edit multiple blocks at once. Right now you can only edit individual blocks via the BlockEdit command, but changing geometry of multiple objects in a single operation - for example changing height of multiple doors could be useful.
Blender has added a similar feature a few years ago, which became very popular (pressing TAB let’s you now edit meshes of all selected objects).
It is already possible to edit attributes of sub-objects in multiple blocks in the latest Rhino 8 WIP (e.g. color, layer, isocurve density etc.)
It may not be the most exhaustive explanation, but one example below where editing multiple different blocks in one go would significantly improve productivity:
You have multiple blocks that need to be extended upwards. With multiple block edit mode you could turn on SolidPtOn for all of them and drag them up. Right now you need to do it for every single block one-by-one.