So you decided to continue the discussion here instead of the other forum (with Bob)?
First off, once you decide to go to an interchangeable lens system, it's more about the len(es) than the camera body. That said, it seems to me that a wide-ish (around 35mm full frame equiv.) fast/bright (around f2.0) prime should be OK for most shots of "landscpaes, family, gathering, mountains, desearts". You could even use a typical kit zoom (say 20-50mm) for everything except indoor/night
Moving on to the specific cameras/questions you listed:
- Panasonic G6 is not available os of now. Do we know, when it is goign to be for sale ?
It actually was for sale for a while, but there seems to be a delay with the second shipment. So I don't think anyone outside of Panasonic knows for sure, but it should be soon. I'd guess within a month.
Are there major difference between G5 and G6
Depends on how you define "major". The major addition to me is WiFi, especially combined with Panasonic's app and a tablet (and "focus peaking" for video). Other than that, the G6 is basically a G5 with a firmware update which enables more features/shooting modes. But since you say "Occassionally will shoot video also and expect it to be good", the G6 would seem to be worth the extra cost. (Note: one of the new features is 24p, and the G6 also has an external mic jack.)
Personally, the only reason I haven't upgraded is because the G6 uses the same sensor as my GH2, except it no longer has multi-aspect mode.
- Olympus EPL-5 - I couldn't found this in stores. Need to check out more stores to see it physically.
It's significantly smaller than the G5/6 and/or GH2. (As noted above, I own a GH2 and I also own an E-PL5.) And the E-PL5's still (photo) image quality is at least equal, if not a little better than the Panasonic cameras. But be sure to factor in lens size. i.e. with a large lens, the E-PL5 will lose a lot of the size advantage. (And although it makes a very attractive package size-wise with a Panasonic 20mm f1.7 "pancake" lens, be aware that this particular combo exhibits banding at high ISO settings.)
Personally, if I'm only going to be shooting stills, not video, I'll leave the GH2 at home and take the E-PL5.
Canon EOS M - Was reading about it and few blogs say that it is having auto-focus problem. Is it true ?
true, but Canon fixed it with a firmware update. (see this youtube video
.) But yes, it is "old", and the rumor is that there will be a replacement announced later this year.
Sony Alpha SLT-A57 - This seems to be bulky.
Yes, because the Alpha SLT line is not mirrorless. For (smaller) mirrorless bodies, have a look at Sony's NEX line.
Pentax - These camera are having very good reviews, not sure which model I should pick to compare. May be K-30 or K-50.
Similar to the Sony SLTs, the Pentax K series are not mirrorless (except the K-01). Pentax Q series are mirrorless.
HTH - Mark