I'm going to expand a bit on what I think is off about the SL.
For Leica to sell a decent quantity of a really expensive camera/system, they need to have our "want-one!" responses to conquer our "too-expensive!" responses.
But Leica does not have retail outlets in many states or even countries. Most camera stores won't carry their mid-to-top-end gear because of the large investment versus their relatively low volume sales.
So, to get that "want-one!" response, Leica must rely on the look of the camera, and how we think it will feel in-hand, to go along with its specs. There has to be a significant "this is a unique camera system that gets it so right where no one else is," to make us consider a camera system purchase that's in the top 1% for cost.
That just isn't there with the SL. The only people who will excessively want an SL will be those wanting an auto-focus FF system, but who somehow think that Sony's A7rII or Nikon's Df are just so wrong as to warrant a much larger, much more expensive SL system. Not many will do this based upon looks:
SL vs. Df vs. A7r II, each with representative FF 50mm auto-focus lenses.
Yes, I'd prefer Leica's menu system. And I'm reading that when enthusiasts get the SL in-hand, they really, really, really like it.
But I'll never likely get an SL in-hand, there are no shops near me where I can go play with one. So I'll likely never overcome the "WTH?" response I get when I look at the above comparison. And I'm guessing not many "M" or "Q" owners (or others) will either.
So, my best prediction: the SL just won't sell all that well.
Nothing controversial for most about this prediction, but I hope I nailed the "well, why is that?"
What new Leica would sell? Well, any camera system that you can just look at, read the specs, and go, "they got it right - while other companies have missed the mark."
Look at the "Q:" competes with the Sony RX1 series, but gets the user interface, haptics, and gestalt so "right" - while the Sony is so "meh" or "pbpblth" in these areas. So, the "Q" is selling even though it's a more expensive camera.
"What's right" is going to vary from enthusiast to enthusiast. But I'll bet enough commonality exists that there are at least two to three other candidate Leica possibilities (right now) that would "nail-it" like the "Q" has. But the "SL" hasn't.