This initial 24-90mm SL lens has internal stabilization. The other native SL lenses to come will also, I bet.Sure. So what? I don't own any, but I can rent them very easily if I need to. I suspect they'll image the same way other lenses of similar focal lengths image, and of course there are few ultra-wides in the right focal lengths for the 24x36mm format. They're not the only option.
I doubt you'll have to stop down at all with the SL. And yeah, it doesn't have IBIS. Neither does my M-P or D750, and neither did my A7. I couldn't bother using any of my M-mount wides on the A7 due to all the color shifting and other crud. There's a device called a Tripod ... Perhaps you've heard of it? ;-)
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G
As to wide prime lenses, the S lens range offers 24, 30, and 35mm, which will fully work "as native" on the SL. It may be a while before we see those focal lengths made for the SL, but the system will fill out gradually. As has the S system for that matter. Not overnight, but there are plenty of attractive lens alternatives now.