In the current version (2.4.6) I am not able to move objects to other modules without losing all associations and references. Will it be possible to move objects from one module to another in the next version of Mendix. This will help a lot while cleaning up meta models that grew too big.
Yes, in version 2.5 you can move objects freely within a project.
Edit: I just saw you were referring to metaobjects. This is already possible in 2.4, just right click them and select 'Move to' in the context menu.