White

Touch the Spirit Realm can un-impend the DSK Overlords, which I think is pretty sweet.

Blue

Having Temporal Manipulation as a duplicate of Time Warp might be too much, but I love Time Warp decks so much I'm willing to give it a shot.

Black

Some subtle but important changes. I'm really excited to include Stitcher's Supplier and give a little boost to heavy graveyard synergies.
In my experience, the sac decks generally don't need Blood Artist, but I'm giving it a shot here.
Demonic Tutor is a no-brainer include for me now that I acquired a copy. It's powerful, but without true combo decks it's not overbearing at all.

Red

Mizzix's Mastery is a blast, and cube is one of the only places to play it.

Green

This looks like a small change to green, but there are significant changes in the gold cards and lands that help green quite a bit. I was getting too cute with green's beatdown plan; a card like Pelt Collector in this powerful a cube is just worse at its job than cards in other colors. So I've moved towards what green can do uniquely - lands, big mana, and fixing. Field of the Dead is in, alongside Golos and Primeval Titan. Atraxa is a great ramp payoff. I've retooled the Simic and Selesnya gold cards to pay off big mana. I've also added some more interesting utility lands like Shifting Woodland that can help cards like Knight or Wight of the Reliquary. I also have my eye on Natural Order as a very powerful incentive to draft green.

Gold

A lot of these changes are to buff green, as mentioned above. Valki to me is mostly a green card with extra utility, and was included specifically for Bring to Light.

Colorless

Boots was a support card for Nadu, but it's a trap card for newer cubers and felt way too narrow.

Lands

I think Sokenzan and Takenuma are the two weakest of the cycle by far, so this was a no-brainer.

Rather than making bulk changes at set release, I like to gradually update the cube as I acquire cards. This makes the history a mess, so here's a blog post instead.

Removing MID/VOW Slowlands like Deserted Beach
I felt like I had one too many land cycles. This could replace the checklands, but they're pretty similar and I feel like the checklands are classics.

Removing Day/Night cards
Nobody wants to track Day/Night in paper. I love me a Suspicious Stowaway, but blue has so many 2 mana looters that I feel less bad cutting it.

Most the other changes are to make room for DSK cards, with a couple FDN/J25 reprints putting cards I already owned onto the Arena client.

White

Blue

Lier is a favorite of mine, but from the first session it seems like counterspells are too important to turn off.

Black

I'm going back and forth on Deadly Dispute vs Village Rites. I like that you can flash back Rites with Arcanist, but I'm interested in seeding more Artifact synergies down the line.
Orcish Bowmasters is an experiment, I'm watching it for power level concerns.
Forsaken Miner is one I picked up from the Arena Cube, it's a very good combo with Goblin Bombardment.

Red

I wanted to try value Underworld Breach for stuff like Bauble/Bolt, but I just can't see it working out. Maybe when Urza's Bauble comes to the client.

Green

Gold

I want to like Shaman, but it never seems to work out.

Colorless

Lands