This was basically my response to a question on the GDS2. I'm not sure how I actually feel about it, but if you think about it it almost makes sense. I think this ability is too ingrained in blue to actually change, though.

Mmm. It also doesn't make much sense when you start gaining control of blue and black creatures. Why would Green be able to control a Zombie, or a Leviathan? The concept of making the creature mindless, then moving it around as an automaton works for Green's enemies, but seems wrong for green. There does seem like the seed of something right at work here, but it would probably be a bit more complicated. I want to say "Creature with power 5 or greater", but it still seems wrong on a large vampire. I could see a 10CC+ enchantment that says "you control all creatures"...

Yeah, I would never suggest this card be printed. It does feel quite wrong. I think it would be much more likely, as you said, to gain control based on power, or to take all creatures.

Yeah, green is not going to get this straight up, but there is some interesting design space here. Green is always short of ways to deal with creatures, and I'm not sure of that is identity, and how much is gameplay balance. Judging from cards like Entangling Vines green should get some removal, but it should very situational, so there may be room for green to get some control -- probably a variant of the ability (like how red gets temporary control and blue gets permanent control).

For instance, to try to capture the "burn out the unnatural animation and return a creature to nature" perhaps "You control target creature. It loses all abilities [except...]" Which is a weaker version of what blue gets, but green would be very grateful for.

Or tie it to the number of forests you control, or the power of a creature you control.

Increase power and toughness, and remove abilities is an option. One of my original ideas was to give the creature defender and turn it into a plant. Problem is, you can argue anything in the color pie is legit if you just change the cards you are working around. Gain control could be White if you also gave the creature Lifelink and Vigilance and called it an angel. It could be red if you turned the creature into a dragon... etc...

Maybe that's legitimate. Maybe we can get away with anything in the color pie, if we add some keywords that make that color happy. I don't know. The argument seems too big for me.

There already is a white version, called Evangelize. In fact, all colors have creature stealing but Green, as far as I know.