Some simple features that would help (not only) underwater enthusiasts:

"restricted focus range" - my older cameras all allowed to limit the auto focus to "non-near" distances, which is a very important feature if you need to focus in water that has a lot of particles in it that confuse the auto-focus.

"make all functions accessible from the menu" - while most camera owners enjoy having a multitude of knobs, every additional knob on a camera that is strictly required for the camera to be operable means significant additional cost and risk of leakage when building underwater housings. Thus, for an underwater user it may be a very good trade-off to access some seldom-used functions more indirectly via a menu, requiring less mechanical holes & knobs in the housing. This is also important for focus and zoom settings - which are especially difficult to address mechanically in an underwater housing. (Of course, the ultimate help for underwater-housing manufacturers is to just integrate a cheap infrared remote control receiver, which allows to access functions from outside a sealed housing without any mechanical holes at all.)

"automatic grey card use": When enabled, recognize a simple pattern that can be printed on a grey card, and when this pattern is detected in an image, use a custom white balance setting based on the greycard reading (for subsequent video and stills).

"do not make timed trigger and bracketing mutually exclusive" - I always wondered why the GH2's dial is created such that you cannot put the camera on a tripod and ask it to shoot an exposure bracket series 10 seconds from now.

But I guess, after all, the most obvious of all requested features are the ones that are also the most unlikely to be realized by any stubborn big corporation: Don't fuck your customers by dongling overpriced expendable accessories (like batteries). Don't cripple the camera to ridiculously low recording bit rates. Therefore, I am kind of sure that no matter what the GH3 will bring, it will take a lot of time and a firmware hack until any GH2 user will have a reason to actually upgrade ;-)

Ah, yes that might be correct. :)

@thepalalias Isn't that how it is now?

Not so fond of the idea of the camera asking if everything is ok upon switching between non native m43 lenses.. As it is now, it is one setting which needs to be selected once. Not an issue in my book.

If it's possible to have some kind of in-cam sync mode via external controller (phone, computer...) that would be useful for many, I'm sure!

If it would be possible to have a 1:1 pixel time limited (more than 1 second though! - f.i. 720p frame 24 frames / s for 20 seconds, 1080p frame for 14 seconds, 2.5k frame for 10, 4k for 8s) burst mode in a few different frame sizes that would be awesome. If possible with raw capture. Don't know what the buffer specs are so this might be a hardware specific request...

+1 for ETC zooming! Turns all my fast primes into parfocal zooms!

Use the physical switches for changing focus, metering modes when in video mode. Why on earth are these menu options on the GH2?

during recording changing iso and wb

One single most important thing for the gh3 firmware is that it must be hackable. A pinch of suspense with some new fw hack protection tricks would be interesting to watch though.

Not sure whether anyone has already said, but - Make every zoom (both 4/3 and m. 4/3) parfocal via firmware, even (or particularly) in manual focus mode.

What do you mean when you say you did it? You mean test patches that were never released?

Yep, during experiments with GH2 30p that was accessible only via such strange way and without audio.

@Bueller Then you should post it to different topic! This IS a topic about firmware! Oh gosh...

An interactive online manual that is easy to figure out.

ps I know this is not firmware related but I wanted to mention it.

@robbie75vr I did not want to limit our dreams :)