First, please leave a suggestion if you have one!  I'm always open to refining a deck to make it win more consistently!  There are always new cards coming out that I either don't see, or see and don't think to put on a list, so helpful input and advice are always appreciated.  Thanks for looking!

The goal is to hit Kaya, Orzhov Usurper's ultimate with enough cards exiled to do lethal damage.  Vito, Thorn of the Dusk Rose accelerates that timeline by doubling her damage up with life loss from your life gain.  Ashiok, Dream Render and Bojuka Bog accelerate your quest to exile graveyard cards pretty quickly once on the battlefield (Ashiok also locks out an opponent's fetch lands, etc, which is a nifty bonus).  Tasha's Hideous Laughter and Glimpse the Unthinkable help get cards in their grave faster for exiling.  The rest of the deck is counter magic, instant speed removal, accelerating Kaya, and exiling stuff, with the goal of filling their grave and exiling it, while keeping your opponent's board in check.  Kaya's -1 is also pretty handy, removing a pesky Chalice of the Void, etc, with ease... modern is chock full of 1/0/Xcc drops that she can remove if needed, albeit that means two extra turns are needed to -5 her.

Whisper of the Dross and Clockspinning (and Cankerbloom) get Kaya to her ultimate one turn sooner, allowing her to pop the turn after you cast her (theoretically you could pop her the turn she's cast if you have five mana available and two of these to cast). And both being at instant speed, they don't tie up mana you might need for a different control/removal card.  The deck needs playtesting, which it has not yet had (no one in my home playgroup plays modern, and... now I live in Cambodia, so...), so the exact numbers for different cards are still in flux.  This is built to last a few extra rounds, while keeping your opponent in check.  A T5 win is certainly feasible, but T6 is maybe the ideal spot, assuring enough mana, enough of the right cards in play, and plenty of control/removal to stay in charge for the wincon.

You might consider putting in Extirpate alongside Surgical Extraction if you feel it makes sense.  The original concept of the deck was anchored on four of each card, which was what brought me to Kaya through card searches, and the rest fell into place around her.  In earlier versions, I had three of each and toyed with four of each.  I think it needs to be sideboarded at a minimum, maybe even have three of each available (total), because they thrive against decks built primarily on four of each card, which happens in modern often enough.  Removing a combo piece from a deck can be crippling, not to mention slowly mana-flooding their deck when each one is cast.

Cankerbloom is in for the obvious extra artifact and enchantment removal, but also the ability to choose when I proliferate with it to pump Kaya, and at the cost of only one mana to activate, making it viable to sac right after casting Kaya (assuming it's already in play).  The obvious main drawback is the total cost to cast and use it, but maybe it's still worth it...?  I feel like more removal was needed.  I swapped it in for some Clockspinning, which is much more cost-versatile, but it's up to you to make adjustments...

Culling Ritual is probably a sideboard must-have, as, aside from Cankerbloom, our permanents cost 3cc.  Stuff like Bogles can get wiped out, or a Chalice of the Void... lots of modern staples cost two or less.

The current build isn't running any red, but eight of the 22 lands produce any color, so splashing red is very feasible.  As such, I'm kind of intrigued by the idea of adding Goldhound as a ramp source.  The problem is the general lack of consistency to have access to red mana early enough to cast it, and the fact you have to wait a turn to use it, making it potentially too likely to be too slow, on average.

Misty Rainforest and Flooded Strands search for Watery Grave and Temple Gardens, allowing you to color-fix outside the lands that tap for any color.  If one were to want to run Ragavan, Nimble Pilferer in the deck, I might add a Steam Vents and take out a Blast Zone, which will give you five more lands (13 total) that can tap for red.  Mix and match the Misty Rainforest and Flooded Strands as you see fit.

I went with 22 lands because almost everything in this deck costs 1 or 2 mana to cast, except for Kaya, Ashiok, Vito and Tasha's Hideous Laughter, which are all 3cc.  But there's no ramp or draw, which pains me.  But what to take out?  Again, it needs playtesting, and while I want to add more draw (Experimental Augury...?) and ramp, part of me wonders if I can get away with not adding any...?

Also, the sideboard is simply a list of options for you to consider in making your own sideboard (it's not what I'm bringing to a tournament).