Floodfarm Verge
Gloomlake Verge
Blazemire Verge
Thornspire Verge
Hushwood Verge
So the opportunity cost of including, say, Floodfarm Verge in a slot where you would otherwise be running a Plains is low but not nil. Considerations:
- Are you running fetchlands such as Fabled Passage, and if so, is this dropping your basic land count low enough that you might run out?
- Are you running enough basic lands that you can reasonably expect to turn these on in most games?
- Are nonbasic hate cards like Furnace Punisher or Sunspine Lynx common in your meta and/or particularly good against your deck?
Overall I think I probably like these better than most of the rare duals that are currently in Standard, although that's "like" in the sense of "want to play with"; I'm not necessarily saying they're stronger in the abstract.
Interesting to note that the cycle depicted here is only allied colors and only goes clockwise (on the color wheel) when adding the second color. There is potential for three more cycles like this one if Wizards wants to make them.