In retrospect, I suspect the last six months of Standard probably would have been better if Kaladesh block wasn't changed to be legal six months longer than it was originally supposed to be...
Guilds of Ravnica potentially represents the biggest upheaval to Standard in years, thanks to Kaladesh block and friends finally rotating. With the rotation comes a manabase possibility table flip. For instance, consider the case of red aggro decks.
Steam Vents and Sacred Foundry are absolutely enormous incentives to splash blue or white in our red aggro decks, assuming we splash anything at all. Besides, the primary draws to black are rotating, anyway.
In evaluating the relative value of a blue or white splash, we need a mono-red deck to provide a baseline.