There are a few ways you can take this:
- Have the archetype be centred in one of the colours e.g. +1/+1 counters in Abzan with green as the primary colour as it's easy to build GW or GB counters deck but WB counters isn't really a thing. This lets you indicate more clearly to your drafters what they should be doing (as unpacking 5 or 10 cross-cutting wedge/shard archetypes in an unfamiliar Cube is tricky) and maintain a colour wheel (so G(wb) gets counters, U(rw) gets artifacts, and so on)
- Ensure that an archetype is well represented in each colour pair within the wedge/shard but in different ways. Artifacts is a great example of this: WR can be aggressive, UW can be control or combo-control, and UR can be based on Welder/Tinker hijinks or something else. This probably works better at a slightly higher power level where the boundaries between archetypes are clearer and cards have more defined roles versus a lower power level where cards are more playable in decks they aren't naturally suited for (and thus where these choices are less punishing)
- Have plentiful manafixing and gold cards with the aim of making those wedge/shard combinations the default for most decks at the table, Shards/Khans-style, with a small amount of overlap in other colours. So your Abzan counters signpost cards could be Ghave and Abzan Ascendancy, but picking up enough fixing could let you touch red for Marath or Grenzo
I've tried starting with the ten shard/wedge pairs, assigning archetypes to them, and building a Cube from there but was never satisfied with the result. Here's where I usually ended up:
WUB: Artifacts felt natural was pretty good as black picked up some good artifact tools in recent sets (improvise, some of the Commander stuff) and Esper had an artifact theme in Shards block; this tended to be based in U per the first point above, but WB as an aggresive artifacts deck was fine. For a more conventional theme, you can try the Solar Flare-style Blink/Reanimation decks: black offers great ETB effects and reanimation (especially time-limited variants like Apprentice Necromancer) plus flickering lets you chain them together in satisfying ways (evoke Mulldrifter + Undying Evil; next turn, blink Mulldrifter...)
UBR: Artifacts are good again here (less so in BR, but you can make that a Welder Reanimator deck or base it on sacrificing specifically artifacts). Spells matter is anchored in UR, but black offers the clearest possible signpost in Kess, some great instants/sorceries to (re/)play, and a distinctively black take on the deck if you pair the creatures that care about instants/sorceries with black's reanimation/Disentombs (Makeshift Mannequin your Torrential Gearhulk which Mannequins something else, or just the Snapcaster + Kolaghan's Command dance we're used to from Modern/Legacy)
BRG: You can try to show whoever bungled the Jund lands Commander deck how it's done by marrying Poxes/Death Clouds and Wildfires with all of green's land fetchers or going off with The Gitrog Monster but, as the Devour mechanic acknowledged, BRG has a lot of creatures and a lot of ways to profit from them and it's hard to go wrong with that
RGW: Great at going wide with tokens and Anthems or going tall with pump/Berserk effects. It's hard to have those coexist and tie them together but if you can (Eidolon of Countless Battles is a personal favourite), it's really satisfying: one of my favourite semi-casual Constructed decks used Akroan Crusader and Vanguard of Brimaz to make tokens and Phalanx Leader or Anax and Cymede to pump them (and one of my favourite actually good Constructed decks used Phalanx Leader and Hangarback Walker alongside Gleam of Authority and other all-stars)
GWU: Blink is safe but uninspired; there's a spells matter theme that white (as always) doesn't support properly but might be worth it. I've tried some wacky Turboland and Enchantress themes in Bant that I liked a lot, especially Turboland (and those two can intersect if you want them to)
WUR: Another natural home for artifacts (basically take any permutation of Breya's colours and you're good) but also the best at supporting spells matter; my favourite form of this is using the instant/sorcery token makers with pump effects that key off the same cards or trigger the same payoffs (Jeskai Ascendancy!! but also Rally the Peasants et al)
URG:
This thread
GWB: Counters, sac, Enchantress, graveyard nonsense,
Pattern... I could make a 720-card Abzan Cube and still run out of room
WBR: Aristocrats is really the only option here, with a possible artifacts subtheme ala the Boros Monarch deck in Pauper; you could try a planeswalker-heavy midrange deck if you want something slower
BUG: All about finicky graveyard stuff, viz:
(Assassin's Trophy, Notion Rain)
This deck is sexy and it knows it
