I'm wondering if its possible to have additional unit frames created in the following scenario.
Picture a healer using Grid/Clique to manage his raid healing. Right above the grid square in a similar fashion 4 additional squares show up (or 3 or 5 whatever) of the players taking the most damage in the current fight.
It basically allows the raid healers, without looking at meters to quickly realize who is taking the most damage (might not necessarily be the main tank(s)). The benefit would be a larger unit frame that draws the attention of the healer and perhaps makes it easier to click on the key players of that fight.
The key idea is to transparently combine damage-taken meters with a Grid-like unit frame.
To elaborate, it's not possible, because secure frames cannot be created or modified while in combat, and only secure frames can target units. You could create frames that looked just like real frames, but you wouldn't be able to click on them to target the unit, or interact with them in any other way.
If you're already using Grid, you could write (or find someone to write) a plugin that interacted with, say, Recount, and added a Grid status for "High damage taken".