So, it seems with 12.04, they're switching back to Rhythmbox, after switching from Rhythmbox a year ago. I don't get why. They say that it's because of a blocking bug in GTK3# (if I understand that correctly), but that's just one bug, and in the same breath they say RB is not well maintained. It seems Ubuntu guys were dissatisfied with Banshee in some way, but apparently the Banshee guys were never notified of any problems.
Also, it can't be to save disc space by dropping mono, because at the same day it was announced that the install disc will be enlarged by 50MB.
Also, isn't it a bit shortsighted to push Banshee for default inclusion, and then drop it again a year later? How is that a sustainable use of dev resources, or consistent? Apparently there was quite some heavy effort by banshee devs - David Nielsen used the term "bending over backwards for Ubuntu" iirc.
In summary: Can anyone shed more light on this?
Related question: Why was Banshee chosen to be the default for 11.04?
Sources:
http://www.omgubuntu.co.uk/2011/11/banshee-tomboy-and-mono-dropped-from-ubuntu-12-04-cd/
http://www.omgubuntu.co.uk/2011/11/rhythmbox-to-return-as-ubuntu-12-04-default-music-app/
http://www.omgubuntu.co.uk/2011/11/ubuntu-12-04-disc-size-to-be-750mb/
http://summit.ubuntu.com/uds-p/meeting/19442/desktop-p-default-apps/
Answer about why Rhythmbox was chosen from the Ubuntu Desktop Mailing list
GTK3 support. "The main reason for this is that Banshee still uses GTK2 and the GTK3 branch is currently blocked by some missing GTK# 3 features. And this blocks porting the Ubuntu One Music Store plugin to GTK 3 and it prevents it from working properly on ARM."
Source: WebUpd8
And you'll probably have better luck on looking for different players on Ubuntu Forums, but since I'm answering anyways, I like Clementine a lot.
I think it is important to stress the usability problems that plague Banshee. This is IMHO the main reason behind the community preference for RB. This thread at the Ubuntu Fora details several of the issues users were confronted with after the inclusion of Banshee in release 11.04:
This return to RB is a coming back to senses, IMHO.
It seems that you also answered the question, at least from the ubuntu developers point of view. That gtk3# bug is enough to make the developers unable to port banshee to gtk3 so it seems it is not that small. I think removing mono from the installation CD is an extra and i'm not very sure about it. Before banshee was included mono was already shipped to include tomboy and gbrainy and i'm not very sure tnat the ubuntu team is thinking of removing them from the CD
Summarizing, i think the biggest issue is the lack of support of gtk3 in banshee, but there's still time to solve that problem