Maybe a dumb response, but what about using a digital camera as a flash meter?
(I'm not sure about how hard the synchronization issue would be.)
It seems that using a digital camera as a flash meter could also give other benefits, such as getting an idea of how the balance between main flash and fill flash is working.
To big (won't go in my pocket), inconvenient (have to move the sync back and forth), imprecise (center weighted at best), and not capable of reading a ratio except as how it relates one to itself. The image could be pretty misleading as film shoulders and toes are curved compared to the virtual absence of shoulder and toe in digi-gizmos. I suppose if one got used to it ala polaroid as a proof medium it could be useful, but only as a proof shot, not really as a meter. Probably would be most useful for chrome shooters, much less so for negative, in my opinion.