I started looking into this and a test build for the current 2.2.2 release is available at https://ci.appveyor.com/api/buildjobs/b4635xc49s55jsr4/artifacts/dist%2FMusicBrainz-Picard-2.2.2.exe
This provides Picard in a self contained exe file, which can directly be started from anywhere. Configuration and plugin data is placed in a folder “MusicBrainz-Picard” next to the exe.
I would like to get some feedback and testing on this. Does the application work for you? Does the application fulfill your expectations to a portable app? Would you like to see something changed?
*) Portable in this context means, the application can be run without installation and the application data is self contained (e.g. does not save config on the system).