I think the X3 will grow in size as most BMW's do. The X1 seems too impractical for me, I can't do much with it. It leaves me in the same predicament as the 135i but with an extra 2 doors.
The X3 was already a good size and if it grows a couple inches it'll suit me fine. I think the 2nd generation of the X3 will sort out all the flaws it once had. Hopefully they offer it with a decent engine too. Ideally I'd like an X5 but it's big money and I'd kick myself for not going all out on an X6. The X3 will be a good compromise if you can't reach for an X5 imo. Of course, I don't think these SUV's will be idael for off-road use... Just something for around town with a lot of boot space.