Lots of options here from Tarkir Dragonstorm, unsuprisingly. A fair few are not quite in the colours they would ideally be in. (Lots of Sultai Counters, Temur "Flashback" etc).
Also there are very few warrirors, so Mardu is likely to be revamped in the medium term.

Anafenza, Quarsi Revenant, Sinkhole surveyor and Warden of the Grove are definite synergy wins, but are likely too strong, so they go to the maybeboard.

Usher turns into Descendant, due to the counters synergy being slightly more valuable than the warriors synergy.
Furious Forebear is a Spirit and Warrior, but its main purpose is the recursion, which is a grixis focus, and therefore not desirable.
Secrets of the Dead turns into Essence Anchor to have a bit wider, but less powerful synergy, and is marginally less do nothing.
Ureni's Rebuff takes the slot of Ephara's Dispersal, making a reactive bounce spell into a proactive one, while still having some synergy.
Winternight Stories seems more interesting than Scour all Possibilities. Also incentivises playing to the board in the slower blue decks.
Wingblade Disciple goes on the maybeboard as a cascade payoff.
While a warrior, Avenger of the Fallen feels a little Feast or Famine.
Hundred Battle Veteran has some nice synergies, although I don't have a lot of keyword counters to make it a 6/6.
Sidisi, Regent of the Mire seems fun, although it may add too much redundancy?
Channeled Dragonfire from Firebolt is the same logic as bounce spells.
Glacial Dragonhunt replaces Magma Opus. Opus isn't getting cast, and doesn't get flashbakced easily enough.
Host of the Hereafter is an interesting counters card, replacing bad cursed wombat/winding constrictor.

All other cards hopefully don't need explanation for now.

Structurally, I am considering changing the 7th XY gold card to the 2nd XYZ gold card, but this needs a bit more time in the oven.
Mardu is likely to just become "Aggro" or "Attacks matters", headlined by Isshin, two heavens as one.

There are probably more cuts to make, but I didn't enjoy Protean Thaumuturge's effect on the game by doubling effects. It was particularly obnoxious makeing a second gremlin tamer. I think the Clone effect is the bigger problem, so it's been cut.

Tidying up of numbers to happen soon.

Synergies don't line up well with cube archetypes. A Few standalone cards are strong (E.G. Stock up) but thery're not necessary. As such, trying verges over Checklands now the cycle is complete.

Will add details later

No major changes, some maybeboard cards for spirits.
Surveil lands to be included, likely over checklands or cycling duals tbc. Possible going up to 6 duals per colour.

Cuts made on the basis that:
Partner withs are not being drafted, this one is the worse one.
Too many black one drops. This is the least interesting one.
Dictate and Deep analysis are the most dull Blue card draw spells, and i think there are plenty of those?

Previous playtest noted that green was lacking ramp. I wanted to add mana dorks that can be relevant in the late game, and broadly avoided tapping for any colour.
Gyre Sage also plays into the Counters synergy deck that hasn't been heavily drafted.

Deathcap Cultivator is probably slightly better than Werebear, but less cool.
Naga Vitalist maybe fits my fixing criterion quite well.

-Ephara's Dispersal is a nice bounce spell, espescially with the surveil adding some synergy, and it playing slightly better in defensive decks.
-Archpriest of shadows has some mild counter synergy, but otherwise is a nice (although potentially swingy) top end for a grixis deck
-Scorn Blade Berserker is just super neat.
-Deeproot Wayfinder is a ramp/graveyard filler.

-Final Flourish is another sacrifice synergy removal spell. Relatively interchangeable.
-Pile On is similarly an interchangeable black removal spell. Not a lot of convoke support, although that's really a bonus here.
-Ozolith is synergistic, but probably too strong.