The relevant MTG cards here are Ghalta and Mavren, and Etali Primal Conqueror
This card does spread that "mill damage" to every player, which can be really potent in itself, but turning off some of those win conditions to mill more feels a bit durdle-y to me
The Battle of Bywater and Dawn of a New Age - Both of these will be showing up in go-wide decks, with Dawn being a better Phyrexian Arena for this archetype
Besides, Ultimate Guard is a Japanese brand, and you know how surgically precise they are
Unlike Izzet, Spacecrafts actually have a better home in Dimir control, particularly if you pick up Susurian Dirgecraft, which comes with built-in removal
I could definitely see changing the third Jace, the Mind Sculptor for a Keranos, God of Storms, as this one cant be killed by Lightning Bolt and a later drawn Red Elemental Blast