SX200 - Feb 2009
SX210 - Feb 2010
SX220 - Feb 2011
SX230 - Feb 2011
So my guess is Feb 2012
I would expect;
Digic V for sure which should lead to slightly better low light performance.
Probably the same CMOS sensor or a slightly tweaked one.
Maybe a bit faster lens but probably the same (14x) zoom range. Maybe 24mm on widest, instead of the current 28mm.
Better video and a few other minor tweaks in the menu system.