I'm on the fence about ST3. It will depend on the breadth of the sample library and the initial price. The enormous shoes ST3 will need to fill aren't those of Kontakt, but of its own predecessor, ST2.
ST2 still gets used here on a regular basis. Not because it's a great piece of software - it wasn't ever the best sampler around - but because of the breadth of sounds included. I'm approaching a terabyte's worth of Kontakt libraries, but I'd need a lot more to completely cover the same ground as ST2.
If ST3 offers what ST2 does, only with higher-quality samples and a bigger UI, and doesn't cost a fortune, then I'm in.