Probably ought to consider tossing in the only plainswalker your deck can actually run Karn Liberated

Cool deck idea, I like it. Since you are running proliferate you could run Magistrate's Scepter if you like extra turns. A Scroll Rack is always helpful. Also Banshee's Blade could be fun too if you like.

As for what to take out, this is just my opinion, but Millstone and Tower of Murmurs don't seem that helpful to your proliferate style. But, if you really like milling people you could always add Grindclock.

Karn Liberated is on my list, but I haven't been able to pick him up yet. Millstone and Tower of Murmurs are just fillers for the time being. Thanks for the ideas!

if you could manage to proliferate 3 times per turn you could have infinite turns with Magistrate's Scepter i would highly recommend that as well.

Since you have Throne of Geth I would also recommend Pentavus, with that two card "combo" you can proliferate for 1 mana and if you have any other sources of proliferate he can get big pretty fast. Also, you can break him apart for Blinkmoth Urn before your upkeep then reassemble him afterwards.

Alas Naked Singularity has a colour identity of WUBRG so it would not be legal in this deck.

Naked Singularity, while one of my favorite cards, is just filler for this deck. I didn't realize that it was illegal, but I guess it makes sense.

Also along with my recommendation of Pentavus I would also recommend Triskelavus both would make great additions