Leica says other Lens manufacturers could join the L-mount world
The japanese site DC.watch had a talk with Leica CEO. He gave away this info about the L-mount alliance:
1) Leica is considering selling Sigma and Panasonic L-mount products in their Leica stores
2) There are yet no plans to extend the partnership yet.
3) Yes, other Lens manufacturers can use the L-mount specifications to make L-mount lenses
via L-rumors.com