Considering how complicated it is to put a folder on ignore especially when that folder is already traked in the repository, I can only agree with mr. j.hughes that a contextual menu item to remove and ignore a file's parent directory would help. GikKraken got it right: in its file contextual menu you can ignore the file or ignore the file's parent directory and it is completely logical, in addition if the file or directory is traked then GitKraken propose to remove the tracking which is exactly what most people want when they discover a file or directory has been added to the repository accidentally.

Maybe tabs could do it. Multiple tabs displayed at the top of the windows, one tab per opened repository. Close the tab close the repository. Switching tab switch the display to the corresponding repository. Easy, efficiant. We could even get rid of the "Repositories" Panel which is seldom used by most user.