Behold the Multiverse replacing Ray of Command to fall in-line with blue's theme in the cube of card draw, replacing the creature-control.

Fleshbag Marauder replacing Bone Picker to more-align with sacrificing creatures instead of having a payoff for creatures dying.

Kazandu Stomper replacing Citanul Woodreaders because green's theme in the cube isn't card draw. Kazandu Stomper allows sacrificing/reuse of lands that synergies with other cards.

Haunted Cloak replacing Signpost Scarecrow because it promotes combat and board presence over color filtering (which is what lands should do in the cube).

Raiders' Karve replacing Spare Supplies because it promotes combat and board presence.

The updates for the cube include new cards from Ikoria, Core 21, Jumpstart, Double Masters, and Zendikar Rising. I might continue to update/upgrade cards from the cube with cards from these sets but I'm relatively happy with where the different colors fall.
Red isn't getting Omen of the Forge because I think Magma Jet is a similar enough effect and that it's better because it doesn't require more mana to scry, in addition to the Instant synergies already present in the cube. Similar justitfications exist for the cards, maybe in the future I'll list my reasoning for adjusting each card.

The next changes for the cube will hopefully involve adjusting Multicolored cards, as there are some cards I don't believe fit within their colors, aren't powerful enough, or don't have synergies with the guild colors.