I don't know, I'm iffy about this. There's already a lot of product identity confusion, and products being too similar at too close a price point, and these updates would make things worse (specifically the 600D, I'm fine with the 1100D).
The 60D hasn't been selling very well as it is, and adding an articulating screen to the 550D would make it even worse. This is a guess, but I'd wage that more people choose the 60D rather than 550D over the articulating screen than say...wireless flash control.