I’ve just updated/upgraded a Raspbian Buster SD card and noticed that it now contains Sonic-Pi 3.1
Running it on a Pi4 now. Not yet fully tested, and it will probably have some bugs that have been cured in 3.2dev, but at least you can run it on Buster now.
EDIT It does not appear to have erlang support or the two osmid binaries.
Consequently there is no midi or OSC support working in it.
You can see this from the log files and from looking at
dpkg -L sonic-pi and dpkg -L sonic-pi-server
So sad.
I offered Raspberry Pi my support if they could fund the work, but they said no. They’ve clearly chosen to do it alone and consequently haven’t done it correctly 
What does this update include?
Depends what you are comparing it to. As far as Raspberry Pi goes, on Raspbian Stretch, which will run on models up to a Pi 3B+, but NOT on a Pi4, you can run Sonic Pi 3.0.1 which includes the use of Midi and OSC communications. This is fairly close to version 3.1 for Mac, and PC.
However, the new Raspbian OS named Buster, was initially release with an earlier version 2.12 which did not support Midi or OSC and was therefore a backward step. Since then a version which uses the source code for version 3.1 has been released and incorporated into Buster, but unfortunately it does NOT implement the commands associated with midi and OSC. This is a potential source of confusion, as the release does contain details of these commands in the help and tutorial files, but they will not work. It does look as if it supports the other features of version 3.1.
The version was not produced by Sam Aaron or with his knowledge.
It is possible to add a full working version 3.1 to run under Raspbian Buster, but at present the only way to do this is to build it from Source. I have a script (as yet unpublished) to do so, but I have also published details elsewhere in this forum to build the latest version 3.2dev on Raspbian, which I routinely use.
Sam comments on the cur down 3.1 version in the previous post.