I was thinking about this just as a joke but then thought it would be slightly more plausible, you have 2 bombsites (or more) and in pl_switch style you choose which one you want to explode, at the bombsites there is a payload cart which takes a minutes (Or however long) to go in a circle round the bombsite and then explode in spectacular tf2 style. I'm sure it could be done if enough effort was put into working it out.
Just a thought.

That's quite interesting, though not quite de_ style. Could be worth a test!

Would be cool, mostly for novelty reasons

Here's a fairly decent idea of De_Dust2, put into TF2. You have to blow up both of the bombsites by planting a bomb (Intel) at each site and waiting 15 seconds for it to explode, before taking it to the next one.

With well thought out spawn locations and timers, could be nice.