Well the problem with Anakin and Palpatine talking in the senate is the lighting. You can change what's in front of them pretty simple. The problem is with the face shots as they talk. The color tone changes about 200 times. So it's pretty hard to replace the opera with anything, unless it's something that has the color of the room changing every 3 seconds.

One second the background is purple, then its teal, then it's (insert 5 different shades in between). Otherwise I would have done this a very long time ago.

It's a damn good idea tho. Just not possible to make it happen without it being obviously altered