Construction
Anyone that follows my posts knows that I favor an approach of writing out all 10 guilds, and developing a theme and sub-theme for each color pairing. This sort of structured design approach helps prevent "cube-designers regret" down the line, when you realize that no one is going into G/R, and now you need to patch in a few G/R decks, hoping that your inclusions/exclusions won't make the cube worse. By having all combinations represented, and a backup sub-theme, you help make sure that you have as broad a gamespace as possible for your drafters to explore, thus preventing (or at least delying) them from solving the format.
Also, people generally don't draft mono-colored decks, so i.m.o it makes little sense to think in terms of "what does my green section do." Your green section will never be played on its own, it will always be supplimented by another color, which will warp whatever it is that its doing. The only exception, I find, is red. Someone will, inevitably, draft a mono-red aggro deck.
The design of this cube also really hammered in the importance of having broadly applicable cards. I think I was knocked off track a bit by MMA and VMA, each which use print runs to enable narrow decks in their respective formats. However, in cube, since you can't use a print run to control the availability of certain cards, every card must be broadly applicable. Its a bit like designing a good sideboard for a constructed environment with a broad array of possible matchups: your cards have to be relevent in many places, not just a few. For example, in cube,
thirst for knowledge is a better card blue draw spell to run to support an artifact theme, than
thoughtcast.
Also, of course, the need to minimize variance caused by:
1. Mana flood (addressed via mana sinks)
2. Color Screw (addressed via the proportional availability of mana fixers)
3. Mana Screw (addressed via bounce lands/cycling/cantrips/cheap TOL manipulation)
4. Poor Hands (addressed via deck building, cycling, cantrips, cheap TOL manipulaton)
Finally, the need to prevent:
1. Board stalls (addressed via evasive creatures, removal, combat tricks, temporary protection)
2. Removal Check/attrition Format (addressed via balanced threats with not
too strong/abundent removal)
Archetypes
The archetypes that I arrived at look to be:
UW: heroic/tempo/Splicers
UB: Control/self-mill
BR: goblin Sacrifice/value reanimator
RG: Midrange Pump/Ramp
GW: Auras/+ + Counters
BW: Control/reanimator
UR: Spells Aggro-Combo/control
BG: Dredge/reanimation
RW: Wide Aggro/Control/Artifacts
GU: Ramp/self-mill
There is some flexibility here, of course. And:
R: goblin aggro
W: white weenie aggro
G: midrange
U: tempo
B: Control
Again, not too heavy of a focus on mono-color, since you will hardly every get a mono-color deck (beyond maybe red). I am ok with three+ color decks being a place of creative exploration, providing that they have a solid 2 color base to build from. Grixis and Esper are natural combo colors though.