White
I don't like white (in this context). It's doing the opposite of what Eldrazi do. It kills big creatures and loves small creatures. There's very limited overlap between a big Eldrazi deck and the entire color white except that board wipes can make the game go long and there's a few playable token multipliers.
I have a few options from there:
Suck It Up
Play a normal 10 color pair wheel where I don't really love WU, GW, and WB. I actually like Boros because it's a simple pairing to go fast and keep the format honest.
KTK Wheel, WBGUR
WB Sac
BG Yard
GU Ramp
UR Spells
RW Aggro
The tricolors are the natural overlaps of those.
Onder Wheel, WRGUB
This happens to be the wheel that Onder runs.
WR Aggro
RG Ramp
GU Also Ramp
UB Control Yard
WB Filler (flexible because it sits between an aggro and a control pair)
Slanted Wheel WRGUB or WBGUR
This seems less likely because it's so weird, but it would focus heavily on xGx ramp and have WB/WR as an aggressive adversary on the far side of the wheel. There would be a decent quantity more green cards as well as some extra xG, Gx, and Wx multicolor cards to support the respective green ramp pairs and enemy aggressive pair. Imagine Odyssey block (Torment and Judgment), but it's Green vs Aggro instead of Black vs GW.
The Green Cube
I like this a lot less than I liked The Black Cube. While black has access to almost all effects at the cost of life, The Green Cube has always felt like The Ramp Cube because ramp is such a central identity to green. When every deck is green, it feels like there's less variation than when every deck was black. Think of GU vs RG compared to UB vs BR. The green decks are different flavors of the same thing, but the black ones are complete opposites.
I have rough mental outlines for all of these and lists for a few, but none are really speaking to me. I was hoping that SOS would clear things up, but it made it more complicated. The enemy pairs look really deep right now thanks to the semi-recent TDM and SOS, but the Onder wheel might be better suited long term.
I'm currently somewhat stuck deciding how to set up my colors to best support the goal here, a mid-high power format where Eldrazi are castable.