This will be our only Xperia rumor today. We promise. And while we have no definite confirmation from SE that a follow-up to the Xperia X1 is in the works, what you see above is a Twitter post from SE marketing guru Harold de Kort. Run through the ol' Google translator, you get "Of course after each X1 is an X2 and X3, X4, X5. What else is new. "
Either that's a bit of a kiss-off answer (which is entirely likely), or, yes, they're working on filling out the Xperia line. (Hopefully with Windows Mobile, but even that's not certain.) And if SE follows the same timetable it did with the X1, we could be hearing an announcement shortly and then seeing the phone sometime next year.