Mollari!
Yes same scene popped into my mind reading the above. Would be cool but I wonder how cool you'd think it was if the AI did it to you? Can't have it both ways

The AI is even nice enough to use traditonal warfare all the time. However flip side - look at the sympathy the Narns got for the bombardment - maybe some sort of diplomatic bonus or aid could be rendered in an effort to rebuild. For instance the bombarded* planets production and maintainence costs are paid for a set number of turns divided evenly between UP members. So an 'Aid' column would appear on the domestic screen.
I'm not sure how this would work if the planet was conquered after a bombardment, but presumably you would not trash the planet you were planning on conquering?
This drain of resources of UP members would cause the diplomatic penalty Lycenae put forward. I don't think kicking civilisations out of UP would be a good idea but sanctions/reparations for war crimes could become prohibative enough that a civilisation willing to use such measures may come to a point where opting to leave UP of their own accord would be the correct course of action due to the economic strain.
Yes I'm looking at you Korath. I think it would also go a long way to highlighting the difference between the Korath and the Drengin Empire - With the Drengin conducting wars well within the boundaries of the UP but the Korath going to such lengths that interstellar pressure forces them to withdraw (and all the penalties that go with it)
* I'm talking about the proposed bombardment changes not the existing bombardment options (does anyone even use those?)