One thing to keep in mind is that a rod that spey casts well in a river is typically not going to be the optimum coastal overhand rod, and vice-versa.
I've watched a lot of people who missed this subtle distinction in their buying practices use traditional action spey rods on the beach, and when the wind, surf or big baits are the order for the day they are holding the wrong tool for the job.
Conversely with the rise in spey rod manufacturers many people have purchased stiff spey rods and struggled with their spey casting on rivers. That rod might have been great in the surf, albeit unnecessarily long.
A rod with authority to throw for distance into wind, over waves and heavier flies; stripping the entire line to tease the fly to shore and fighting big fish in sloppy surf... is not even close to being a sweet river spey rod that lofts a tight wedge over the pool. This is particularly true if you are spey casting on the river to fish where there is little backcasting room - that rod is quite different than a surf flyfishing rod. So in my humble opinion, the best tool for each of these situations is worlds apart.
But to answer your question, I think it's possible to find a rod that suits both purposes but it will be less than ideal in both applications, and the advantages will be reduced in each so that a single hander would be arguably just as good due to the compromises made to find the middle ground.
Admittedly, if a person fishes estuaries with currents and inlets, rivers with small flies and lighter lines, they could use the same rod for both applications of course. But enter the word "surf" and things change dramatically.
Production samples ship to me tomorrow
Once completed final QA, production will begin.
FYI - I will need help getting the initial order investment together so am offering a special discount to early adopters in exchange for feedback and possible phone interview. This program is limited qty and time only, once dealers are signed up the program will end.
I'll provide details privately, just email me or PM to participate.