I'd play 4 of these in most of my multicolor decks. Most of the times it's just Command Tower, except for the rare time that your opponent machine-guns your mana base. (Both those situations are bad, to clarify.)

Mm. I don't know if you ever saw Glimmervoid in action, but it was very, very good, providing Affinity decks with that much needed mana of their choice. In theory, the Glimmervoid player could get screwed if you destroyed all of affinity's artifacts... but at that point, you destroyed all the artifacts. The loss of Glimmervoid barely mattered.

Illusory City looks a lot like that in my mind. I could see why it's a risk in 5-color control, but in the admittedly rare 5-color aggro deck, it's a boss card. Maybe that's okay? Personally, I think encouraging 5c aggro isn't a terrible idea.

That said, I don't know many spells that target your land that doesn't also destroy them. Sure, sure, Gigadrowse could be devastating. But outside of a few cards like that, most people won't have the answer. I don't know if "But they could pull them up from their sideboard" is a good design argument, either.

Not so much 5c aggro as perfect mana for 3c aggro like Naya or Jund, and making it easier for them to splash a fourth colour like Dark Bant.

This is too strong, clearly. I wonder whether something that works off the more frequent ability to target creatures could work. The straightforward version ("Whenever a creature you control becomes the target of a spell or ability, sacrifice ~") has interesting deckbuilding constraints, but is probably far too easy to forget on a crowded battlefield.

I just tossed this card out because it randomly occurred to me. I didn't really think about how powerful it would be. This is why I would never be good on a development team.