So many variables you will need to take into account. From the top of my head:
Flex in the PCB,
possible breakage in the PCB,
the glue holding copper to the fibreglass shearing,
the solder joints shearing,
warping the plastic housing,
whether the BNC is bolted to the housing or not,
the material the BNC connector is made of,
the wall thickness or the BNC connector.
That said, I would think they would be able to hold a small amount of weight, but if you have something heavy, I would suggest connecting it with coax, and not leave it hanging.