You can now export whole modules to file including forms, Java actions etcetera. That module can then be imported into another project. Usually a form depends on entities, images and other resources and exporting just the form does not make sense.
Note: in 2.5 you can move items to other modules simply by dragging and dropping in the project explorer. Exporting and importing forms/microflows was often done just to move a document to another module. This is no longer necessary.
In the final 2.5.0 the export and import of single documents (microflows, forms, etc.) will be available again.
Nice functionality, but I use the 'save as file' a as kind of versioning system. Customers tend to revert to previous versions every now and then. Are there any versioning and comparison features in 2.5 or planned?
Right now you could use the 'export to' functionality to make backups, (or just quickly move your form into a temporary module and export the module). Versioning and comparison are on the roadmap, but will not be available in 2.5.0.