I got a chance to hold the SL tonight, but the battery was dead so I didn't get to use it. Here are some initial impressions:
- very solid - like Nikon D4 solid, like it was carved out of a block of metal
- a bit larger than I had envisioned from pictures
- I have broad palms, so even though the camera was large, it didn't come down far enough to make it comfortable to hold and the bottom edge is sharp so I would need to add the vertical grip that makes the package even bigger
- the 24-90 lens is HUGE - like Nikon 70-200 f/2.8 huge if you have the Leica hood on it, at least that's the way it felt to me. This makes the SL with the zoom really big. This is not a camera/lens for street portraits, it would scare people the same way a big DSLR does.
- I mounted a 50 APO M to the SL with the adapter - this makes the APO seem toy-like in size, but the weight balance is nice
- I put it next to my Sony A7R2 and the SL (without the vertical grip) is bigger than the A7R2 with the vertical grip mounted
- I am not sure what camera bag I own that would fit the SL - it would never fit where an M240 would fit even with just an M lens on it
- I can't comment on the operation or the viewfinder - that will have to wait for another day, but it's going to be hard to replace my A7R2 since that has 42 megapixels and in-body image stabilization and the SL is 24 and has no stabilization
- Aside from autofocus lenses, I am even more puzzled now what the whole point of the SL is. Perhaps the SL2 or SL3 will have 50 mpx and stabilization and more lenses by that time (especially primes).
I tried an SL body today, looking at it as a possible replacement for my M240, since I typically use either wide angle lenses, or longer lenses close to wide open (i.e. with live view). The 24-90 is just too heavy / bulky, as is the camera itself, compared either to the M240 or, an alternative compromise, the Sony A7rII that you mention.
I thought that the focus peaking was much better than the Sony (and the EVF slightly better), as was the ability of the buttons, etc. Although the M240 is an attractive camera, being able to focus without having to recompose, is a big advantage since particularly the faster Leica lenses have idiosyncratic focus fields.
While I agree that it is good to get back to basics, for me the basics include being prepared to carry the beast. This starts with the M lenses, which are the lightest available for full frame, high quality, but not AF (or weather sealed). I am not wedded to the rangefinder experience, nor do I mind too much whether the viewfinder is optical or digital.
I remember when the D3x emerged with an amazing 24Mpx and finding that I needed to step up shooting my discipline, not to say retouching patience, to get rid or all the dust and blemishes that were invisible at 12Mpx. So while having extra Mpx, such as 42, is welcome, it is not really what makes the biggest difference to me.
Nevertheless, for the time being, I am skipping the SL (which has only limited native lenses for the next year anyway) and hedging my bets with a combination of the (i) the M240, when I am land/cityscaping with wide angles (although I have not, in practice, found the corner performance of the A7rII with wide angle lenses to be an insurmountable problem, and (ii) the Sony A7rII when AF is beneficial (notably people shots): the Zeiss or even Sony/Zeiss lenses are very good indeed.