Idea I had, not sure of wording. Basically use this to exile a land and from then on it has all abilities of that land stapled to it, adding more as each land is exiled. Thoughts?

I don't know. I realize that this is mythic, but compare it to Encroaching Wastes. Repeatable land removal is so strong, and frustrating. If this entered untapped, cost a lot less, and exiled your own lands, maybe it would be okay. This might be interesting:

", : Exile target land you control.
­: Activate each other mana ability of ~ without paying their costs."

Mmm, yeah - as it is, this is just "Destroy one of your opponents lands each turn"

Exiling your own lands, and activating ALL of their own abilities? Sounds exciting, but; um, you could just NOT do so, and activate the ability of the original land? What does putting all your eggs in one basket actually gain you?

I guess it makes Juniper Order Druid etc. incredibly scary.

Maybe it could exile land cards from your graveyard.

from graveyard may be a good idea maybe any graveyard too. Main Idea was that it could 'pretend' to be any land exiled by it so you could activate it as any one of the exiled lands each turn.

My only issue with the current design is the strength of repeatably exiling your opponent's lands.

Yeah, the Necrotic Ooze meets Thespian's Stage is great fun. The Stone Rain every turn rather less so.

Okay reset it to exile lands from Graveyards at a slightly reduced cost.

Looking at this again, now that the lands are exiled from graveyards, I think it can be much cheaper (probably just to exile one card). Alternatively, something like ", : Exile all land cards from target player's graveyard" could be a fun twist on it.

Question: Would this be more interesting with the ability to exile land cards from your hand as well? That version combos massively with Lotus Vale and Scorched Ruins, but even this version is pretty good with those cards.