well, it is a key question - timing when you jump into a camera upgrade does make quite a difference - when the OM-D came out I waited for the X-E1 with a firm intent to jump one way or the other (bought X-E1/18-55 and haven't regretted it).
One thing you can guarantee is at some point the X-Pro1 will not be Fujifilm's top camera.
Perhaps a minor point for pro's but I knew I *really* wanted the 18-55 with a compact form-factor, so an EVF was going to be more important for me than the OVF and with my objectives being compact/EVF the X-E1/18-55 is actually a better camera (for me) than the X-Pro1/18-55.
Having said that, Jan/Feb and Aug/Sep seem to be the big camera announcement periods (X-Pro 1 & OM-D EM-5 Jan/Feb, Canon M & X-E1 Aug/Sep) so it's a lottery when the X-Pro1 will be replaced. There's no hints on the rumor sites though so maybe Jan/Feb is unlikely - Aug/Sep 2013 wouldn't be unreasonable and would be my bet.
It's easy for people to put a wish-list together of what they'd like to see in a new camera - it seems to me sometimes these are presented as some kind of its-a-dead-cert-the-camera-will-have-this (and the Canon M community basically got f-all of their pre-announcement 'wishes'). But if I was to guess, an X-Pro2 would add an EVF at least as good as the X-E1 - I'm not sure if any other enhancement would be substantive - the X-Pro1 was the landmark product that created the category. Maybe phase-detect focus on the sensor would be added, but that risks compromising the X-Trans so we'll see. Either way the X-Pro1 will be a good investment for a while.