Well what they do is just add wee bootloader code to Android 2.4 and that's it (yes Wildfire S will get 2.4 update for sure)
I've been trying to get info from HTC about a possible update, at least to 2.3.5 but the guys at tech support are too vague and didn't even reply to bug reports I sent them. I have the latest European RUU and it has some problems with force closes after installing apps from Market, gave the guys all my phone info, yet still they don't know if there are plans to upgrade the phone.
However they promise that they'll let me know as soon as they know something and also say that they want to guarantee the best possible user experience.
I guess ICS 2.4 would be perfect. Now that it's officially released I suggest HTC to Get on their Boots (like U2 would say lol).
The WFS has enough hardware to run ICS so what are they waiting for?
I've had so many phones from HTC and even QTek (former HTC) that I expect some level of commitment on their part.
Sorry for the long post. Needed to uncompress my thoughts... ;-)