As per the title…I can try and make one but would much prefer an official version
I’m just curious @RaspberryDave : What would be the advantage to have Picard running on a Raspberry Pi?
You know that Picard is a music tagger written in Python with a GUI. Why should I attach a keyboard, a monitor and a mouse to my Raspberry Pi just to tag my music files?
If you would ask about “Raspberry Pi MusicBrainz server please” I would say: Go for it!
This depends on the distribution you are using on your Raspberry Pi (e.g. Arch Linux ARM has Picard in their repository).
We don’t even do the packaging for x86 based systems (with the exception of the Ubuntu PPA), so I don’t think there will be official packages from MusicBrainz developers for any Raspberry distribution.
But it is quite easy to install Picard from source. And if you decide to build a package and keep it up to date you could share your work for others.
As @outsidecontext says, it’s already here. I’ve used Picard on both a Raspberry Pi 2 as well as on my ODroid-C2. If it’s not available in the distribution you’re using, then you should bring that up with the people making packages for that distribution.