This is a new idea inspired by another uservoice that was declined:
https://plasticscm.uservoice.com/forums/15467-general/suggestions/10300338-remember-last-entered-path-for-workspace

However, the solution suggested here supports all three of the conflicting scenarios given by Codice staff when declining the earlier uservoice: a proposed initial default path (set on first install), a configurable root path (now set from GUI) and a way to remember the last entered path (but only on demand).

There is a setting DefaultWorkspaceRoot in file guiclient.conf, but there is no way to set that from the GUI. I propose adding a link/button "Set as default path for new workspaces" or similar in the New Workspace dialog, next to the workspace path box. When you press that button the mentioned setting should be updated with the currently entered workspace path (minus the filename). That way a user will not have to manually edit this setting in the .conf file, but on the other hand it will not be overwritten if you temporarily use another path for a new workspace.

NOTE: This feature would be similar to the "Set as default query" used elsewhere in the GUI, so it should be consistent with the overall style...