Having making many changes and then spending time with my list as a whole, here are a few more updates.

Overall, I have trimmed cards that I overlooked in my original update. For example, Chillbringer feels a bit out of place as Elementals are no longer part of the simic deck. Instead, I have Shipwreck Dowser helping any blue deck recur their tools.

Otherwise there are some cards that I have either discovered or remembered, which I feel now are a better fit, fill a gap, or that are too cool not to try. For example, Light up the Night being a bulk rare is an easy replacement for Searing Barrage, plus it add some redundancy for Red players seeking burn. Or, Awakening of Vitu-Ghazi replacing a big Green dummy to give Green some instant-speed spice.

Having tuned my Gold signpost cards for each archetype, here are the changes I've made in each colour pair. Similar to the Gold, Colourless and Lands update, I am being more strict in refining each deck's archetype. Some notable changes are ridding of Wolf and Element typal and committing to the Populate and Land Creatures decks respectively. In a general sense, I was quick to cut on-board•instant-speed•effects, as I acknowledge my Cube aims to play cards that most might be unfamiliar with.

Green had the biggest and most numerous changes. It hurt to cut some of my pet-cards, but my goal is ultimately rewarding synergies rather than drafting and casting the best spells.

I made one more swap in the Izzet Gold cards, giving access to the new Young Pyromancer that is Third Path Iconclast. I think that Izzet will need playtesting as I am unsure if the deck has a balance between go-wide with Balmor, Battlemage Captain, or stick one or two prowess creatures and then play interactively.

Finally, instead of adding four more utility lands, I added a second copy each of Evolving Wilds, Terramorphic Expanse and Ash Barrens. The 450th card in the list is a second copy of Cogwork Librarian, just to shake things up!
Next is to playtest!

In general, this update is of course to upgrade using newly released cards that fit my archetypes, but also to trim the cards that don't fit synergistically.
This session included updating Lands, Gold and Colourless cards.

First, an easy change to my landbase was upgrading from Trilands to Triomes. Through playing in paper, I've decided to trim the Vivid lands cycle. I've added Prismatic Vista, but I am still looking for four utility lands to replace the other four Vivids.

Then, to truly focus my Cube's archetypes, I cracked down on my eight Gold cards per colour-pair. This is where I was more strict with trimming pet-cards and committing to a deck's intended play style, rewarding synergies. Boros remained unchanged, but some highlights are committing to Azorius Bounce, focusing on Adventures. I decided that Simic can be the ramp deck to support multicolour decks, but will also aim to be a deck that wants to make Lands into Creatures and swing. I will point out that in the Selesnya Populate deck, I am undecided if Armada Wurm should be either Rhys the Redeemed or Advent of the Wurm. I am unsure about Rhys as I don't want to send the message to a drafter that the Selesnya deck aims to go-wide with small tokens. I love Advent as a card, but I think a creature spell is overall a better selection for my Cube.

Finally, Colourless remains . . . weird. My cube does not have an artifact-focused deck and so my 30 colourless cards are picks for most decks. Fixing in signets, Solemn Simulacrum and other classics remain with some new additions. Aside from mana fixing, ramp and cards that all decks would play, are a number of cards that either fit in one or two decks. For example, I am accepting that Lucky Clover is basically an Azorius card, Desolation Twin might as well be the Populate deck's top end and Diamond Mare finds its home in the Orzhov deck, but could be in anyone's sideboard as an option against aggro decks. The changes made to my Colourless pile commit to this idea of some colourless cards being intended for specific decks. In short, the rationale is to aid redundancy for certain archetypes due to the size of my cube. It might not be optimal, but its my cube!

Finally found motivation to tune the list.

• Added a reach support package in G after finding lots of fliers getting through. UR/WUR still seems powerful. Added Arasta to directly counter this deck after playtesting with @endblink.
• Ditching full 'adventures' theme in WU. Focusing more on blink effects.
• BR had a bigger focus on equipment & knights, but the NEO equipment creatures inspired me. I will return to this colour pair when I need to. Focus is still on attacking with menace, equipment is a bonus. Embercleave is now costed 4RB.
• Other minor oracle changes include Consider > Surveil 1