Hey Ed, I thought I'd put a point of view to this - it's not a spoiler at all. How obvious is it that the character that acts as the antagonist is going to be Trevor, a) He looks evil, b) he is described as being vile, psychotic etc - take this quote from the guardian who are quoting Dan Houser;
And then out of nowhere, the idea of Trevor came to us. He is the guy who does everything awful, relentlessly! He has his own charm, but he … he's a relentless maker of mischief. Not without some principles though, but totally different principles to Michael – an exact opposite take on what it means to be a protagonist in a GTA world. Michael is more about ego and Trevor is more about id, I suppose".
Now they aren't saying you are explicitly playing someone who is the antagonist, more rather a different, fresh take on the gta world, with Franklin described as the typical protagonist, and Michael a man at the end of his career, acting as mentor. Anyway, it seems we are being very informed about it, rather than it being a spoiler - and I don't know about anyone else but as soon as I saw Trevor I thought he looked evil.
It's all in the game...
Project Spark is here.