As of WorkWithPlus for Native Mobile 15 all our Design Systems are based on the Design System object.

With this, you will now have three Design System objects in your KB, one that contains all the base classes with the WorkWithPlus for Native Mobile layouts, and in the others, you can add your customizations for each platform, so when migrating versions, we will keep the base classes updated without losing your customizations, which will be in <KBName>iOS and <KBName>Android objects.