Probably a “good” ISO 2500 would suffice for most people’s needs. Leica said they could do this with the existing S2 by changing the read-out configuration (do-able via firmware) and the result would be around a 2-stop improvement. If they would take it a step further and add a binning option (i.e. – like Sensor+ on the Phase gear), then we’re probably at ISO 2500 without re-inventing the S2.
Another reason I’m itching for higher ISO is so that Leica could release something like a 50mm F4 S. The chief design goal should be “compact”. I’d love to have a lens in the 10-12 ounce weight range that could be used for snapshots, casual walking about, etc. The S2 itself as a camera is pretty light; it’s the 70S that bulks it up – and then of course the hood… 45mm would probably be the preferred focal length since that would equate to a ~35mm FOV. I would prefer 50mm, but that’s just me.
As for the second wheel – I want EC adjustment on the fly without having to press any buttons. A second wheel is the most common way. I’m sure Leica would make it programmable and some people may assign ISO to it. My biggest gripe with the interface is all the various button taps to move around and review parts of an image on the rear LCD. Touch screens are a mixed blessing, but the one the Phase IQ backs is awesome for reviewing images. I don’t need a wheel, thumb-stick and touchscreen – just one of them. Leica can choose and I’ll adapt.
While the S2 is expensive, running a 2nd kit to fill the gaps is expensive too. If the S3 would improve in ISO (both lower and upper), AF speed and some minor ergo tweaks, then I think the S could be my only camera. I would still want something small and some of these new compacts like the Sony RX100 look impressive. If Leica just warms up the S2 with a minor ISO tweak and calls that an S3, then I wouldn’t upgrade either. But if they hit most of wish list then I would seriously consider upgrading. A good trade-in program would make that decision easier.