"Cares about all lands being tapped" is something Magic has tapped into before... these cards were not playing all that well and are best forgotten.

Additionally this has only a single outcome: Ramp. Far too narrow for a keyword mechanic.

I hate to say it, but you're probably right about this one. It's lingered in the back of my head as a weak point of the set. I think there is some genuinely cool design space for it, like Sinkhole Hydra, but this idea is weak overall.

I've struggled to come up with an interesting mechanic for green in this set that fits with my fantasy: An arid, barren world that has been robbed of its mana and is slowly recovering. Barren to me embodies the flat empty spaces that seem to go on forever.

That said, I'd love to hear any other green mechanic ideas you might have!