Mission: Design a Johnny land.

Hmmm. Deserted Temple, not able to tap for mana on its own, and only breaking even on a Karoo (tap 2 lands to get 2 mana). Yet curiously versatile on other things. Lets you charge certain storage lands twice a turn... lets you get double duty from Cabal Coffers or Crypt of Agadeem... Doesn't let you do anything special with Magosi, the Waterveil as far as I can tell, but I might be missing something there...

I've been trying to think of any nonlands this works especially well with, to make it worth playing over Deserted Temple. It doesn't do much on Elvish Aberration (add 1 mana compared to if this was a Forest). It lets you double-charge Black Mana Battery and friends. It gives a Guardian Idol expensive vigilance. It looks like it ought to be awesome with Pili-Pala, but I don't think it is...

It lets you get double activations out of something like a Llanowar Elves you've put Power of Fire or Elemental Mastery on, I guess?

Mission successfully accomplished of making a Johnny card, anyway :)

Do you think it would be safe to take off the , since it doesn't have its own mana ability?

Hmm. That would make it something like Reflecting Pool, but stronger with Karoos / Fertile Ground / etc. Reflecting Pool was somewhat dominant in its time in Standard, but that was partly due to its downright unfair interaction with the Vivid lands which this doesn't share. It'd likely still see tournament play like that, so it depends on whether that's what you want.