I like the new implementation. I nearly never want to go from prone to immediately full upright and I appreciate that my stance keys have been reduced from 3 to 2 so i can have my combat pace toggle closer to my base keys (C). There is a great solution tho... They already have "Go Prone", so just add "Crouch" and "Stand" and change the existing binding to "Stance Toggle" or something similar, that way you have the option of going either way.

I didn't really like the new config, and I switched back to the standard zxc from ArmACO and ArmA2. Just my comfort zone I guess.

I, for one, welcome our new control scheme overlords. It recycles that one key that becomes meaningless, since you are in a certain stance already.

I use ESDF so I have my own config for both A2 and A3. I don't mind there being a toggle, I just think Stand up is the wrong key for it. If anything, it should be Crouch.

Is there an option in the controls to set a key for stand, crouch, prone and then just unbind the toggle key?

Yes you can assign retro zxc keybinds. Im very happy with them since they reset high/low, step lean modifiers for that stance. So when im in high/low standing or lean, i press c and switch to normal stance. Very comfy.

I like the controls how they are. I think some people just can't handle change.

I use this the same way i used it in ArmA2, ArmA1 and in OFP.

My standup key (space) toggles between crouching/standing while my prone key (ctrl) only toggles that. Works nicely that way.

Also, the fact that it remembers the sub-stance allows you to preselect the correct substance before you stand up. Makes effective use of cover much easier.
Changing this would make things complicated!

Easy fix:
Options > Controls > Presets > A2 Commands Layout

I like how is it. Just download stance indicator and you will be fine in 1st person view.

You're confusing "Stand up" with "Up"

Only the "Up" key behaves as you describe and alternates between standing and kneeling (it's intended to work as a toggle crouch command).
"Stand up" on the other hand is not a toggle key and works only in one direction, always reverting the character to the upper stance.
So you simply need to bind "Stand up".

By the way, the "Stand up" command presents inconsistencies across the various stances because in two occasions (from low crouch and from high crouch) it doesn't revert to the default stand up stance.

As a side note, the "Up" key (toggle crouch) has the same inconsistencies and here's a ticket for that:

http://feedback.arma3.com/view.php?id=4057

you can re bind your keys its already in the game

just rebind keys, as house says