We already run wasteland, Mishra's factory and some of us run thespian stage to provide the "new colorless" mana, so that should not be too much of a concern. The Envelop part seems like a corner case but could definitely be useful(we are not the type of deck that keeps mana up often), the exiling a creature seems like the best mode but still a worse Disfiguremost of the time but they both hit Deathrite Shaman which is big, making a token seems to be the least likely to be used.
None of these modes thrill me but the versatility of having all 3 modes is nice. I also think GB Pox has more options with Abrupt Decay and Golgari Charm so it will probably be a much better card for mono black pox.

