There is much talk, and I have listened...
- Oct 25, 2017
Haaaah this is what I meant by people ignoring, this what that wall of text I posted on the other page did - basically, you need to convince Hubert that it's in Edelgard's best interests to tell Claude (using future knowledge and possibly Future Byleth's corpse), then you go to Claude and convince him he can accomplish his ideals safely with Edelgard's help, then go to present Edelgard with the fait accompli that Claude already knows so she needs to trust you and him if she wants it to work out, then all of you go to Dimitri and get him to sign on by promising him the head of Those who Slither. The plot comes from a) Rhea not being on board with blowing up the Crests under any circumstances and b) Those who Slither noticing that they've lost control of Edelgard (or at least that she's started assembly an independent powerbase ahead of schedule) and they move to counter that by seizing the Empire and fomenting revolt in the other territories.Even with time travel, there would have to be a LOT of changes that would make a 5th route like that to be able to work.
One major one being that without context of each other route, it would be even more confusing than the current 4 route-story-split ends up being.
The other being that even with time travel, Edelgard and Rhea are the lynchpins on making the story progress (and TWSITD, but it's not likely you'd ally with them)...and Edelgard hates Rhea because lizard people. Meanwhile, Rhea pre-timeskip, is more than willing to go Seiros on the unbelievers.
I'm not sure how I could see you convincing Edelgard unless you pick up the BE house and/or get access to all three houses - and even then, you would have to drastically change Edelgard's mind somehow early on, and/or incorporate her into dealing with Rhea without somehow triggering an immaculate one appearance.
So unless you time travel either back to Edelgard being kidnapped and 'save her' (after the crest is put in), and/or you somehow defuse Rhea way back in the Nemesis days, it would take a helluva lot of writing to somehow make things come together.
If they were ever to make a golden route, though, they'd have to find a way to 'defuse' edelgard (either make a united house with dimitri and claude, or somehow gain her trust super early on and convince her to change her mind somehow), and gain Rhea's trust.
Theoretically, this could be accomplished by having TWSITD become a much more visible/bigger threat....but I'm not sure what would draw them out into the open so early on in the story.