See Bountiful Pasture. I had that idea first and they're rather similar. The activation here is possibly too cheap, but I wanted it to be exciting.
Alex, we're going to need a new mana symbol soon for our colorless-producing cards. :-)

Not sure if I actually like the new mana symbol. MaRo's argument seems to be that colorless vs generic trips people up, but I don't believe that.

I like it. It clears up potential ambiguity, and allows cards with costs like the new Kozilek. I've had trouble explaining generic mana costs to new players in the past, so I think it's a change for the better.

Also, we can now see things like devotion to colorless, which wasn't previously possible.

Oh yes, I realised last week we'd need that symbol. I'll try to get it in before Christmas.

I'm on the fence. Wizards used to distinguish between generic mana (which has always been ) and colourless mana (which used to be spelled out, as on Archaeological Dig, Millikin etc). Then they gave up and started using the same symbol for both, which didn't seem to cause much trouble.

Conceptually it makes sense to distinguish between a permissive "one of any colour" and a restrictive "one that's only colourless".
I'm just put off by the amount of errata that's going to be applied, including to cards like Blighted Gorge in the large set immediately preceding the small set that introduces the symbol.

On the other hand, I've been in favour of Wizards applying big sweeping errata in the past. Assuming the game has many years of future, the choices made now should always be primarily motivated by what will let the game be the best many years into the future.

My current feeling is that ◇ is a pretty ugly symbol. I don't know if that feeling will last.

I haven't followed the spoilers, when I first saw this, I assumed <> would be an eldrazi-specific sort of colourless mana, like snow. But if Mystic Gate is reprinted with it, I guess they're definitely going with that as a a symbol for colourless mana?

It seems to make "colourless mana matters" make sense in a way that seems obvious in retrospect but I hadn't really considered.

I never really got why the distinction between colourless and generic mattered. Why didn't the rules just use "colourless mana" everywhere, and assume coloured mana could "downgrade" to be spent as colourless mana whenever you wanted? Admittedly, if they'd done that, they'd need a different symbol for "can ONLY be paid with colourless mana" but they could use <> for that anyway if they weren't using it for colourless mana.

I know the colourless/generic thing was confusing sometimes, but I thought it would be simpler to explain by erasing the distinction, not reinforcing it. But in general, wizards are better than I am at guessing what's simple, and more resistant than I am to errata, so if they say this is better, and worth errating every colourless producing card, then I'm going to assume they're probably right...

The symbol itself looked good to me when I thought it was Eldrazi-specific -- a bit scary and spiky. I'm not sure if I like it otherwise, but I guess I'll probably get used to it.

I like the symbol because it's so plain and unadorned. It's just a few steps away from being an empty circle, which is what I had envisioned for a colorless symbol.

And Alex, adding this symbol to cards is entirely nonfunctional errata — it's exactly like the "dies" errata, or exile.