There will be another Fiesta ST but Chris is correct as there won't be anything for about 10-12 months.
I'd watch this year's Motor Shows carefully though, also, take a much closer look at the interior/exterior shots of the Fietsa concept car that was shown now that the actual Fiesta is on sale, that'll give you some clues.
There is alot of new hardware being added accross the Ford range very soon so expect all the specs of current Fords to change quite considerably this year.
In regards to whether you should wait, that all depends on how good a deal you can get on buying one of the last ST150s.
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2011 Focus 3-door Zetec 1.6 TDCi.
Previous <img src="/images/graemlins/stemo.gif" alt="" />s - 2006 Panther Black & 2007 Red. Gone and quite forgotten <img src="/images/graemlins/lol.gif" alt="" />