I'm taking a "wait and see", but I'm intrigued having seen the E3 trailer.
My bet based on what we see is, Vault 76 is a control vault in the sense it's not the subject of a Vault-Tec experiment, but it's almost certainly going to be under Enclave control, either to provide a post-war labor or military force. The Enclave is going to be heavily involved, based on the presence of what appears to be a crashed torus station and the Greenbrier hotel in the trailer; The Enclave's end goal was space colonization (hence the torus), and the Greenbrier is the site of the Project Greek Island bunker which would have been Congress' continuity-of-government emergency site in the event of nuclear war, much like Raven Rock was the Pentagon's.
Now, here's where thing's are going to get interesting...and cool. We see a bucket-wheel excavator in the trailer, and those are predominantly used for coal mining. West Virginia being coal country, after all. What's the Enclave's interest in this region, particularly? The coal -- the Enclave is reliant on fossil fuels, and West Virginia would be a strategically-critical region for them due to its coal reserves. The Enclave's reliant on fossil fuels, rather than nuclear, after all (see, FO2 with the oil rig).
Yes, coal can be turned into liquid fuel. The process is pretty much exactly the same we use for processing tar sands and shale oil in the real world today, except coal has to be liquified first. It's dirty, expensive, dangerous, highly polluting, energy-inefficient, and in the real world cost-effective only for the sky-high price of crude oil, but it can be done.
Now, it'd be cool to play as the Enclave. But, I bet the story will be much more rote, "Enclave are the bad guys, let's go liberate vault dwellers, and save ghouls/mutants". Which, to me, is thoroughly "meh", but I'll still hold out hope to ally with the Enclave.