... what's next an X7 and an X8? I'm just wondering what markets these are aimed towards...

X1 - the folks that want an SAV, but don't need more than 2 doors
X2 - the folks that want an X1, but need 1 more inch of shoulder room
X3 - the current X3 folks
X4 - the folks that want a sportier looking X3 in 2 door form or the the folks that want an X6 need something smaller
X5 - the current X5 folks
X6 - the folks that want a sportier looking X5 in 2 door form