On Linux, the temp file approach has some room for improvement. We are using visualino in a classroom where each kid has his own user and it is common that a computer is used several times without a reboot. What happens then? If user A uses visualino and the logs out, when user B logs in and tries to upload to the board, the temp file (/tmp/visualino/visualino.ino) already exists and belongs to another user. This may be related with some already opened issue!
No error is shown, because file already exists, but it is not overwritten, so project from user A is always compiled and uploaded to the board.
I am not sure how to solve this keeping portability always in mind. IMHO, in Linux I would put visualino.ino file in /run/user/1000/
Yeah, that 1000 is the current user ID, so temp file must be computed at runtime. But my guess is that a similar approach would be nice also at Windows and OsX.
I propose removing temp config path, and compute a user temp path at runtime.