I took Ramunap to a 3-1 in a daily with many outs to a 4-2 in the Challenge (that had other deckbuilding issues) so I can give some preliminary thoughts to the card. I played it in a hatebears deck powered by 4 Ancient Tomb, some Elvish Spirit Guides, and on-color Moxen/ManaCrypt. In hatebears, 3 feels like the right number: it felt marginal against blue, given artifact mana, blue's access to basics, and a propensity for the PO versions to combo out early. It felt very good against Shops, both defensively and proactively on the Wasteland axis; ditto for Dredge, but assuming a Wasteland and less margin-for-error.
In the end, I don't think it has sufficient value to justify a second color all by itself. If the hatebears base color is white, I'm not sure a blue (black?) splash wouldn't be better in the long run. The only other green cards I ran was Deathrite Shaman which I wasn't a big fan of for being slow and lacking punch as a graveyard management tool, and 3-4 sideboarded Manglehorns, which were fine but not as devastating as hoped (better against Shops than PO which will default to the Tinker game plan). If Gush had been unrestricted, I also would have played Gaddock Teegs.
In retrospect, compared to hatebears, I think it might be best suited for the (B)UG-still decks previously mentioned earlier in the thread. Having just one Wasteland source makes the card far more powerful so a good draw engine is indicated to increase the likelihood of finding one. He can attack, of course, under the Landstill soft-lock, and blue decks offer better filtering when his effect would only be marginal. Hatebears or Eldrazi wouldn't want to play GSZ, because of the taxing issues and the lack of targets. I have no opinion of the card in other shells.
Last thought, and don't underestimate it: he makes the value of Jitte go up for deckbuilding purposes.
I saw your list on Goldfish and was hoping that you and the MODO person were one in the same. Thanks for your feedback! By any chance do you have a quick and dirty guide for how you boarded against your matchups during the daily?