It's quite annoying when making a video or screenshot of a creation to have the blocks flashing because of focusing on them with the mouse, therefore I propose a "nothing" mode, when you press the "nothing" button (It'd be toggle) you no longer are able to place or delete, or select blocks. So the crosshair disappears and on rolling over blocks nothing happens, much like when you go near the unbreakable base blocks. "n" would be a good button for it.
Technically spectator does this, I'd say if it were more of a don't interact with those blocks mode, like how when a sword can't break blocks but with other tools or similar to adventure mode but in a creative like way so you can test it out might be a good idea. While this would benefit more with mods with special differences to those blocks or fluids properities more so than Vanilla and how it does things I think that could be suitable. But again, if swords do it and spectator I'm not sure of another suggestion/continuation for ideas to expand/support your idea.
I guess I'm probably thinking of a 'what does this do/what outcomes are there for this block' idea which you could easily do with just looking up the wiki, using the debug stick, using a mod to find out mob/ore info instead. I'm just coming up with ideas here but either way I'd say something could come of your idea or others I just don't know how.