Yes it would be 🙂
Visualization is always a difficult topic... I'm not sure about that, but a callback would be nice.

One idea that comes to mind (this is of course limited to DataFrames), but think the git diff , where I imagine 3 independent section:
Removed columns (+ truncated preview of removed values) (see below) Added columns (+ truncated preview of removed values)
The middle column is then a bit complicated, but I would see some kind of "shared columns" dataframe, where each cell (that has changed) would be split into two - one original value (in red?) and one new value (in green?)
New rows would have --- as original value, deleted rows would have --- as new value (or some value that indicates "does/did not exist")