The new(ish) enchantment from Dominaria called The Mirari Conjecture is a saga-type enchantment with 3 effects:
1. Regrowth an instant
2. Regrowth a sorcery
3. Pyromancer Ascension (copy all instant and sorcery spells that you cast) until the end of the turn

An interesting interaction with this card is that the second effect of the Saga can return Replenish from the graveyard, and Replenish can return the saga. The final stage of the saga will copy the Replenish meaning that your opponent needs 2 counterspells to stop the loop from going off.

The other interesting element of this interaction is that you can cast Gifts Ungiven for Replenish, Conjecture, Enchantment A, and Enchantment B. At minimum you will get enchantment A and B, because if your opponent gives you Replenish or the Saga you will eventually recur all of it. Gifts Ungiven is also a powerful instant you can return with the first stage of the saga. If you have Replenish in your hand already you can just Gifts for 4 Enchantments.

The rest of the deck is going to be a mostly generic UW control deck. The balance of cards seems difficult to choose exactly because the deck wants a certain number of instants and sorceries for The Mirari's Conjecture to work well, but also wants a lot of enchantments to get a big replenish payoff. You also want a certain density of cheap enchantments so that you can use Serra's Sanctum to accelerate your 4 and 5 mana spells.

Spreading Seas seems like an okay card at the moment because it's quite disruptive vs Depths/Post/Eldrazi. It's a cheap cantripping enchantment which helps for Serra's Sanctum and keeps the blue count up for FoW. Another card that has been getting a lot of hype from enchantress players recently is Estrid's Invocation. A commonly suggested use for this is to copy Abundant Growth as a draw engine while being able to copy other enchantments as needed. This list probably won't play green but you can get the draw engine aspect by copying Spreading Seas, and Estrid's Invocation is also nuts with The Mirari Conjecture. (ETB copy conjecture, return instant, upkeep blink copy conjecture return instant, move to mainphase return sorcery).

Opal Wave seems like a solid choice for the A+B combo (unfortunately there is no double-enchantment equivalent of e.g. RIP-Helm that just wins the game afaik) and then the rest of the deck is just removal, disruption, maybe 1-2 wincons.

Maybe this idea is too durdly/stupid but it seems like it could be a fun thing to try, and if you get time to set up it seems like the lategame clearly goes over the top of most things. Spreading Seas seems like an effective way of attacking a lot of the bad matchups for miracles.

20 Land (Strand, Tundra, Island, Plains, Serras Sanctum)

Enchantments
2 The Mirari Conjecture
1 Compulsion
4 Spreading Seas
3 Estrid's Invocation
1 Opalescence / Starfield of Nyx
1 Parallax Wave
2 Porphyry Nodes
1 Sigil of the Empty Throne
1 Solitary Confinement
2 Cast Out
1 Exclusion Ritual / Reality Acid

Instants
4 Brainstorm
4 Force of Will
2 Enlightened Tutor
2 Gifts Ungiven
1 Swords to Plowshares

Sorceries
4 Ponder
3 Replenish
1 Council's Judgment

SB Options
Stony Silence
Grafdigger's Cage
Leyline of Sanctity
Back to Basics?
Unburial Rites + Fatty