Panasonic today announced the not-so-secret 12-35mm f/2.8 GX Vario zoom lens for the m4/3 mount. This lens provides m4/3 with its first fast aperture, high-quality mid-range zoom. I've put the full specifications for the new lens in the database section of this site.
The lens was first leaked in late 2011, then shown behind glass in February at the CP+ show in Japan, and now announced, but it won't actually be available until August (and here in the US, we'll probably have another lag in availability as is usual with Panasonic's market-focused distribution). Thus, one is led to say that, while this is news, it's not exactly news you can act on.
Yes, the announcement of this lens (plus the leaks of its unannounced brother, the 35-100mm f/2.8) does indicate that the lens lineup for m4/3 is further filling out and becoming more complete. No, you can't put it in your bag today. Or later this spring. Or this summer. Maybe this fall, depending upon what country you're in.
I expect this to be a very popular and in-demand lens, as coupled with an E-M5 you end up with a very competent setup that can reach into lower light conditions, but with far less bulk and weight than the crop sensor DSLRs, let alone the full frame DSLRs.
Note: there will be some that claim that 12-35mm f/2.8 for m4/3 is the equivalent of the 24-70mm for full frame cameras. From an angle of view perspective, this would be true, but from a DOF perspective it isn't. The 12-35mm shot at f/2.8 will produce about the same picture as the 24-70mm on a Nikon D4 set to f/5.6. In other words, more DOF. See this article on equivalence for more.