My main theory that changes how we count Shallan's Ideals is that Shallan said an Ideal as she killed Testament. It would explain which swords she's using in WoR and how they are working.
1st Ideal— Same for all Orders. She said this early in her childhood.
2nd Ideal— She said this first to Testament. It was probably simple and childlike, given her age, maybe “I love you” or “you are my (only) true friend” being all alone in the Davar House. My theory: Lightweavers earn their Blade at 2nd Ideal, not 3rd. We've seen Windrunners and Edgedancers earn blade at 3rd Ideal (WoR for Kaladin, Edgedancer for Lift). Some don't even bond a spren until later Ideals (like Skybreakers in OB). Bottom line, Orders progress at different rates and makes sense from a Cultivation-based viewpoint (she would like variety in progression).
2nd Ideal— "I killed my father" is said to Pattern. This means that he's now a blade by the end of TWoK but can’t manifest yet because he’s weak in thinking and complex ideas. He can't even manifest physically until Shallan draws his pattern in the beginning of WoR. This means that Tyn is killed by Testament. In the moment before killing Tyn, Shallan notes:
Notice: "But for her, it didn't have to be ten". I think "her" refers to Testament, not Shallan. Testament doesn't need to be summoned in 10 heartbeats because she is still partially bonded to Shallan. We also know deadeyes can be summoned in less, such as with Maya and Adolin (I think they got down to 7 beats). Right at this point Shallan begins to create Veil to hide the past about Testament (confirmed in RoW). The moment of her using Testament after all these years is what pushes her to make Veil, since that action of using Testament is what starts to bring the memories back.
3rd Ideal— My theory: "I hate you" is said to Testament. Yep, Shallan broke their bond as she swore the 3rd Ideal. Testament feels shame for letting Shallan kill her mother and accepts these words as truth, that she knows Shallan truly hates herself and Testament. It would be a great twist, since we wouldn't think that you can swear an Ideal while killing your spren. But Testament is the only one who needs to accept the Truths, and she does if moved to shame.
3rd Ideal— "I killed my mother" is said to Pattern. This was said after the Oathgate transfer, so Pattern had to have been a sword at that point already. This fits with the idea that Cryptics can be a blade by the 2nd Ideal. There is not nearly enough Investiture in Testament for her to do that, being a deadeyes; she can sometimes help soulcast and be a Blade, but that’s it. She moves slower than Pattern does in the Cognitive Realm, so Shallan running to the Oathgate and activating it at end of WoR might've happened too fast for Testament to keep up with her. We also know deadeyes move slowly and keep their distance from their Shardbearers (Maya walking a ways behind the group in OB). Shallan has no need to summon her afterwards, now that Pattern manifested as a Blade already in the chasms and again for the Oathgate, AND Shallan acknowledging how Pattern is different than other Blades, so she finds no need to summon Testament again. The transfer occurs and Testament is left on the platform in the Cognitive Realm, the mysterious island in the east where she was found by the shopkeeper (RoW) and held with her after that.
4th Ideal— "I'm terrified" is said to Testament in TWoK. These truths to her are still pretty simplistic because Testament is from a childhood bond. This grants some soulcasting for Shallan but it's still very weak. By the end of WoR, there's a that WoB says Shallan is on 4th Ideal. He's referring to this one, not any Ideals with Pattern.
4th Ideal-"I killed [my spren]" was said to herself in Kalak's study. Pattern has not yet accepted this (or maybe did offscreen but that seems weak), because he didn’t hear the truth. Remember, she forbid Pattern from following her to Kalak's house.
5th Ideal— This will be a one-and-done truth, a bridge between her bonds with the two spren. It will heal Testament and propel her to 5th ideal for both bonds. Testament’s Ideals revolve around shallan as a child while Pattern’s exposes her childhood, so 5th Ideal is a combination that satisfies both of her spren, and they both accept it. This makes it plausible for Shallan to sweat a single Ideal in the next book.
Thoughts?