MTGNexus

I made like 10 or 20 cycles of trilands. All sorts of different drawbacks. Conditions to enter untapped, conditions to add mana, life loss or additional costs. I came to the conclusion that they don't make such cycles because they would inevitably devaluate all duals and all lands that add any color.

Yup, pretty much. Especially if they're fetchable.

Understandable. There are some existing trilands (Murmuring Bosk, Tournament Grounds, Arcane Sanctum and friends), but they all either enter tapped or have very harsh restrictions.

I don't think that it would be impossible to create a reasonable cycle, but its presence would strongly encourage 3-4 color decks in limited and standard (depending on the rarity), which is usually abnormal. Still, I'm a fan of greedy multicolor limited formats - some of my fondest memories of limited involve absurd four color decks backed up by a ton of fixing.