Emergency Weld to replace Pit Keeper:
This is effectively a 2 mana Grave Digger, and if you're ever in a pinch, a way to stick a roadblock from a lethal attack. It not being a creature makes it an interesting twist. It combo's effectively well with Archaeomancer for looping shenanigans. Pit Keeper did well holding the fort but being able to return a creature OR an artifact without restriction is just too good to pass up.

Wasteful Harvest to replace Chatterstorm:
Without the right support, Chatterstorm can never reach its full potential, effectively being a waste of space. On the other hand, Wasteful Harvest can fetch more than creatures and lands, sowing the seeds for delirium or similar strategies to blossom in the future.

Fallaji Archaeologist to replace Augur of Bolas:
This card digs for the same amount of cards as Augur of Bolas, hits more than just instants and sorceries. Only time will tell if this is enough to support newer strategies.

Bitter Reunion and Scrapwork Mutt to replace Thrill of Possibility:
Drawing cards in red is no longer just a possibility but an actuality with the introduction of these cards. Izzet spell based decks have better draw engines in blue so there is no real loss here. The transformation of card types to permanents gives Boros bully more tools to play with and potentially open the door for cards like Unholy Heat to make an appearance.

Rust Goliath to replace Murasa Behemoth:
What's bigger a Goliath or a Behemoth? Well a 10/10 is certainly bigger than an 8/8 and while one does come down a few turns earlier, the purpose is to be the biggest thing on the board. Something neat for green is that prototype creatures also synergies with flicker effects, allowing the flicker strategy to expand into green as the secondary support colour.

Gaea's Gift:
This is a combat trick that keeps on giving. With two mana up your opponents will be in for a surprise.

Gixian Infiltrator and Goblin Blast-Runner to replace Stirge:
These two cards are perfect in the Rakdos sacrifice/aggro archetype. Gixian Infiltrator and Goblin Blast-Runner can sneak in extra damage with all the amount of incidental sacrifice effects in the cube and not having to be specifically creatures. Stirge will no longer eat up a 1 MV creature slot in black, which is already full of more powerful cards.

Creeping Bloodsucker and Ossuary Rats to replace Blight-Breath Catoblepas:
Looking at where you would want this effect, usually from behind Ossuary Rats is better and Blight-Breath Catoblepas is a stinker. Creeping Bloodsucker if left unchecked can close games and make it really difficult to kill you.

Nomad Decoy:
A good card that would slot in very well in turbo mill decks in white. Threshold is very easy to achieve without the need to introduce self-mill effects.

New reanimation spells in white and self-mill effects seem very interesting and could be a new area to explore in the future.

Boulderbranch Golem:
This hits less like a branch and much more like a boulder. It is a fantastic card for midrange decks as it allows you to catch back up on life which could make or break aggro matchups.

Very strong removal however the discount would have to wait quite a while on and isn't very effective when you're being overwhelmed by aggro decks. Prison sentence is a huge upgrade to Arrest, but if you were to judge it against the other removal spells white already has access to the verdict is quite clear on why it didn't make the cut.