I don't think that we will find that the are from things *very* different from what we're already postulating. They are short powerful explosions from far away. Just the nature of their shortness means that they have to come from something that is less than a few light-seconds across. This pretty much narrows the options to things smaller than stars as the source of the explosion.
Originally Posted by RussT
I doubt that we will find that they are from the final seconds of evaporating cosmic strings, or from Z-pinches from chaos in the magnetic fields around accreting SMBH's, or brief looks down the exhaust jets of alien spacecraft.
GRBs are associated with the formation or merger of very compact objects. There are certainly variations possible within this theme.
Forming opinions as we speak