Hi Simard,
Unfortunately there's no way to import locations into the Windows 8.1 Maps app through KML files or other bulk mechanisms. We understand that it is important to you to have a way to get all your locations into the app in a quick way so that they can be available everywhere so I'll pass this feedback to the team.
You can also submit this or other new features requests in the feature suggestion forum: https://windows.uservoice.com/forums/265757-windows-feature-suggestions/category/87866-maps