Van Buren would have been an interesting experience, if only so we could see where the series would have gone before it was sold. I know there is a lot of stuff in the Fallout bible and Van Buren itself was pretty fleshed out in terms of story, but it would have opened up a lot of potential new plotlines. The whole backstory involving Presper, the closure of Sulik's search for his sister, the origins of the New Plague, all unfortunately forgotten and left to the archives now. I did enjoy New Vegas, recycling some of the storyline as it did, but the eventual outcome of the battle of hoover dam didn't really progress the Fallout storyline for me. I find it difficult to accept the 'new' canon, project purity and synths and all, and always wonder what could have been.
Any fan project that could capture that sense of mystery would be massively appreciated. Even homages and fan-fiction can have their own satisfying story arcs.