I have had this idea floating around in my head for a while and finally got the chance to test it a bit over the weekend

1 Scalding Tarn
4 Prismatic Vista
4 Flooded Strand
5 Island
5 Plains
1 Tundra

4 Brainstorm
4 Ponder
4 Force of Will
4 Swords to Plowshares
2 Enlightened Tutor
1 Council's Judgment
2 Replenish

4 History of Benalia
3 Estrid's Invocation
4 Spreading Seas
2 Counterbalance

1 Soothsaying
1 Dovin's Acuity
1 The Mirari Conjecture
1 Sigil of the Empty Throne
1 Detention Sphere
1 Cast Out

In the past there have been versions of Miracles that play 4x Mentor in the maindeck (https://www.minmaxblog.com/magic/201...or?rq=miracles). History of Benalia performs a similar function. History has a lower ceiling, but an important consideration in the current format is that with so many planeswalkers (Wrenn, Narset etc) it is important to have some early creatures that can pressure these. If you tap out for Mentor and they Bolt/Decay it then you lose your entire investment. With History you at least get to keep either a Knight or the enchantment itself.

Estrid's Invocation has seen some play in a green-based list that is a more familiar Enchantress-style deck, but the limit in that list for things to copy was something like Oblivion Ring effect, Abundant Growth (draw 1), Doomwake Giant, Enchantress's Presence. Even then it is still quite good, because a Phyrexian Arena that draws 1 on etb is already pretty strong and the additional utility is relevant. But with History of Benalia it becomes an overwhelming threat. An important thing to remember is that Invocation blinks in upkeep but Sagas tick up at the start of the mainphase:

Turn 3 History, make a Knight
Turn 4, tick up History get a Knight, play Invocation copying History make another Knight, attack for 2
Turn 5 blink Invocation copying history, get a Knight, tick up Invocation, get another Knight, tick up History to 3, attack for 3x4 = 12
Turn 6 you can choose to blink Invocation to copy something else or go to stage 3 and attack for 5x4 = 20

If you have 2 Invocations both copying History then you can keep blinking them to copy each other. They will never be sacrificed because they never reach stage 3 and you get 4 knights every turn.

Spreading Seas is included to increase the density of enchantments that do something on etb (for Estrid's Invocation). It also keeps the blue count up for Force and can be a hurdle against heavy-multicolour decks while providing 'removal' against annoying lands like Port/Depths/Cavern/Post/Boseiju etc. Copying an aura doesn't require a target, so with Invocation you can often hit fetchlands with Seas or force the opponent to crack them at awkward times.

Then we have 2 Counterbalance, which functions similarly as in normal miracles with 4 BS 4 Ponder, we might be lacking extra cantrips like Portent but there is 1 Soothsaying to help stack the top of the deck, and 2 Enlightened Tutor to help find it (or to directly put whatever cmc on top of the library to counter a spell). Enlightened Tutor can also help to find Estrids Invocation or any of the 1-ofs (or SB cards).

Dovin's Acuity was originally meant to be a fun-of, but 2 life per turn with an Invocation is actually quite significant and even outside of enchantment synergies the card itself is not terrible in a UW control deck with Plow and Brainstorm

Detention Sphere and Cast Out are just some reasonable removal options
- Sphere: 2-for-1 potential, Pitches to Fow
- Cast Out: can cycle if no targets (flexibility, Replenish), flash (important vs Depths etc), cmc4 for counterbalance

2 Replenish can never be too bad because History naturally sacrifices itself, but they also act as big haymakers against any deck interacting with you with removal or counterspells.

The last weird card is 1 Mirari Conjecture, which is already ok in a UW control deck with instants (FoW, Brainstorm, Plow) and sorceries (Ponder, CJ) but it also forms a loop with Replenish to give infinite instant/enchantment recursion. Because the third mode of Conjecture copies Replenish the opponent needs two counterspells to stop it.

In testing the deck was surprisingly solid. The biggest hole was against resilient creatures that normal UW Miracles decks answer with Terminus. The Sigil of the Empty Throne was also probably win-more. Some alt wincon is probably necessary as people may try to extract History to leave you dead in the water, but this can be put in the sideboard.

So for additional removal options maindeck, it would preferably be an enchantment for the utility with Tutor/Replenish, and something that can answer TNN/Mom.
Options are:
- Humility (strong vs certain decks but disables the strength of History of Benalia, could be a good SB option)
- Solitary Confinement (Hard to maintain and doesn't actually remove the creatures, again could be a good sb option)
- Doomwake Giant (Extremely powerful card, Invocation synergy, but adds a vulnerability to Plow and requires a 3 colour manabase)
- Porphyry Nodes (Has dis-synergy with History and could be very annoying in situations where you don't want to return it with Replenish, although maybe you would be so far ahead in the game at that point that you wouldn't care. I also just realised that on an empty board in this situation it would die with the History triggers on the stack anyway. Good SB option again).

I don't think going 3c is a good idea at the moment (and I can't think of anything other than Giant to justify the splash) so I will try -1 EmptyThrone +1 Porphyry Nodes.

The sb is still a WIP but some obvious inclusions are probably:
- Grafdigger's Cage (it's still valid for E-Tutor and unlike RIP it doesn't interfere with Replenish / Conjecture)
- Stony Silence
- Seal of Cleansing
- Back to Basics
- Some extra wincon like Sigil of the Empty Throne or Sacred Mesa
- Humility

Then some more fringe picks like
- Solitary Confinement
- Rule of Law/Nevermore/anti-combo stuff

Then generic options like Surgical Extraction or Dovin's Veto or whatever

Let me know if you have any thoughts on the main or side.
I wasn't sure if it was correct to play any other nonbasics like Serra's Sanctum or Hall of Heliod's Generosity