Both, Olympus and Panasonic will announce their new Micro Four Thirds stuff on Monday September 17th. Yes, exactly in one week!
Panasonic will announce the GH3 (full specs here), the 35-100mm f/2.8 X lens and very likely show 2-3 more prototype lenses behind a thick glass. One of them should be a fast tele lens.
Olympus will announce the E-PM3 and E-PL5 PEN cameras with same E-M5 sensor. There will be a 15mm f/8.0 lens-cap, the 60mm macro and a 12mm Black limited edition lens. May more prototype lenses will be shown.
More m43 stuff is coming via Sigma, SLRmagic and other third party companies.
On the competition front we know that:
Pentax will announce an unexciting new Q10 camera this week (more info here).
Sony will announce the NEX-6 and three new NEX lenses on Wednesday September 12th (more info here).
Samsung will surprisingly not announce any new NX stuff (more info here).
Nikon and Canon will have no major mirrorless related news. The only interesting thing may be their cheap FF DSLR which will set a new mark on the price of FF bodies (more info here).
Hasselblad may announce a large sensor mirrorless system camera on September 18th (more info here).