Since years there are rumours that Rhythmbox will be replaced by Banshee as default application in the next Distribution-Release. Are there any plans for it to be replaced? The information that I have found is ambiguous.
This hasn't been finalized yet. You can see on their whiteboard though that it's on the table for discussion: Ubuntu Blueprints: Desktop Application Selection for Maverick It comes down to several issues not only with the quality of the application, but it's size (for LiveCD), dependencies, and upstream's development cycle.
This shows a running log of discussions and inputs. As is noted at the bottom Banshee has some issues in the Upstream which might prevent it from making it's way into 10.10.
Banshee will become the default music player in 11.04 (Natty Narwhal). See also the whiteboard at https://blueprints.launchpad.net/ubuntu/+spec/packageselection-desktop-n-application-selection (please don't edit!).