When you've got the money, add Yawgmoth's Will and Omniscience. Dig Through Time is sure to let you cascade into something big for a much lower cost thanks to delve

Beacon of Tomorrows may be good, for recast ability and maelstrom wanderer hits it. Also not against Expropriate but not a huge fan of it neither, could be good you are guaranteed at least 1 extra turn and can steal win cons and or cards that are stopping you from achieving yours from your opponents. Time Warp and Time Stretch i really like because they hit the graveyard instead of being exiled, ik both are up there on the pricy side but are good additions to the deck,

Mind's Desire is a card that is cheap and it should really be in this deck, especially since cascades count towards your storm trigger, i mean this is a storm deck, this being 1 of the best storm cards for edh,

Mizzix's Mastery is another card i could see being really good in this deck, but is high mana cost, since its overload ability is the best part of it, the only problem with it is exiling your cards could backfire on you, that being said though, by the time you cast mizzix's mastery you should have so many could cards in your graveyard that casting them all should just win you the game.

Aetherflux Reservoir is good in here, and can be an extra win con, or just keep you alive

Gamble is my least favorite tutor but it is fairly cheap now, on the other hand Vampiric Tutor is a bit pricey, works well with cascade and is most have if you can or are willing to buy it.Personal Tutor is a more expensive mystical tutor and hits only sorceries but is also really good in this deck considering you will be searching for sorceries most of the time, and because you place the card you searched for on top of your deck it works well with cascade. Long-Term Plans is cheap tutor that is really strong in this deck

Aggravated Assault is a relentless assault on a stick, making it a must have.Fury of the Horde I know is expensive to cast,(possibly not the worst thing with cascade) but it is another card that allows for a second combat phase, and can be cheated out 4 free (other than cascading into it) how ever unlikely you would do that or even be able to, it still is a possibility. Savage Beating is really good in this deck but i think it might not work if hit with cascade

Howl of the Horde I feel like is a most have in this deck, even though it doesn't work with the cards that give you extra combat phases, but it does work with the extra turn ones.

Volcanic Awakening is another storm card but is actually pretty good in this

Also Insurrection is a fun little card and can win you the game,

Talent of the Telepath is really good , and since you will usually have 2 or more instants or sorceries in your graveyard its spell mastery effect goes off..Temporal Fissure is just another storm card.

Clout of the Dominus and Lightning Greaves / Swiftfoot Boots to protect yidris

Time Reversal seems ok in this deck, of course its better version Time Spiral is much better and more expensive

Omniscience is goodAkroma's Memorial is goodCoalition Relic is goodi really like Dolmen Gate in this deck Illusionist's Bracers are really good if they work with yidris's abilityMirari is ok Sword of Feast and Famine is a more expensive Bear Umbra plus some just without totem armor, Trailblazer's Boots is basically a cheaper cmc version of Whispersilk Cloak minus shroudDig Through Time high cmcCall to Mind is pretty goodEcho Mage is good, but hard to use in non mono blue decksSphinx of the Final Word is good in this deckCharmbreaker Devils is goodIncreasing Vengeance is good

And I know you usually would be against board wipes in this deck unless they don't effect your cards, but Blasphemous Act is an excellent one and has a high cmc so it hits almost all things in your deck, on that note i have to recommend Cyclonic Rift even though I'm sue there's a reason you're not to running it. Devastation Tide maybe because it hurts everyone but allows you to recast cards and if you already hit someone with your commander you have cascade triggers which allows you to rebuild quickly

not against Mystic Speculation since scrying can be useful when cascading, and this lets you not only replay it over and over again but lets you scry 3 witch is really good Soothsaying is another good scr effect, plus some, Sylvan Library , ScrollRack and Sensei's Divining Top are more expensive cards that do similar things as this

you dont have to read my earlier comments, they are kinda long, I checked the important ones to be suggested

I'm not a fan of Animist's Awakening in EDH, even less so in decks that go heavy on Cascade mechanics. I'd cut it for Murderous Cut, as it's an efficient removal spell that you could cast for B and still get a good sized Cascade off of.