I didn't know there's a name for this approach but that's what I did in my last campaign, as well.There's a concept known as Schrödinger's Gun. It's kind of an amalgam of Chekov's Gun and Schrödinger's Cat.
The idea is that, until such time as you tell the players what happens, anything can be changed.
Basically, I used a 'turning-point' adventure in which the party's decision to negotiate with the aboleth instead of trying to fight them led to the opposing faction (i.e. the mindflayers) being the 'bad' guys trying to overthrow the world. Until that point I hadn't decided anything and was intentionally vague and ambigous.
Likewise, their search for allies was completely open: I had thought about a half-dozen factions and my players decided who they wanted to try to win over (which included a faction I'd not thought about in advance).