It is going to take longer for the music to start playing.....8, 10, 12 seconds...hard to say. This bothers some folks and not others.
If you are considering moving the iTunes folder over to the Time Capsule, you might want to think about how you plan to back up what is likely a considerable investment in your media collection.
In other words, your "master" library will be on the Time Capsule. If the Time Capsule has a problem, you will lose the library if you don't have a backup on another hard drive.
I would recommend that you consider an alternate approach:
Move your iTunes folder over to another hard drive that is connected directly to your Mac via USB or FireWire.
Access to the libary is much faster this way. And, you can set up Time Machine to back up both your Mac and the hard drive....so you have "original" files on one drive and backups on another.