The Leica SL works best with M and R lenses. Since Leica and Panasonic have collaborated on Panaleica lenses and compact digital bodies for years, the FF Panasonic may well be built to be friendly to M/R lenses, but the emphasis is going to be L-mount AF lenses.
Leica CL and TL/T also handle M lenses well, since their crop factor poses no corner problems (as all WA M-lenses did on the original Sony A7). However, My A7 Kolari handles M lenses fine, and you can have a used A7 Kolarified for about $400, whereas the cheapest SL body I’ve seen is still $3400, and no one yet knows whether this Panasonic will play nice with adapted M lenses.
Sigma for its part plans to build a FF Foveon L-mount body. (Imagine being able to adapt M-and R-lenses to Foveon resolution! Maybe their developing software will improve as a side effect.) They plan to shift their production emphasis to L-mount, phasing out the native SA mount while providing L-adapters for SA lenses.
In any event, it’s nice to see the spirit of collaboration among these companies; maybe we’ll benefit from a sort of Velvet Revolution in camera/lens compatibility. I’m pretty committed to Leica and Sigma these days, so will be following L-mount development with real interest.
More detailed discussion can be found on Leica Users Forum—search for “L-mount”—and presumably on Panasonic-/Sigma-centric fora too, as well as the usual rumor-mongering photo-clickbait sites.
