The current objid format is the object's dbref, followed by a : (colon), followed by the object's creation time, in seconds. For example, #7:841701384. It is assumed by design that it will be impossible to destroy and recreate an object in the same second.
The objid format is intended to be extensible. A natural extension would be to include another colon and a unique identifier for the MUSH on which the object was created, in order to provide an identifier that is unique for all time on all mushes (this would require a secure way to uniquely identify a mush, however).