People keep ignoring my time travel 5th route idea and it's makin' me sad lol
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.
He really should have been recruitable post timeskip alongside Fleche to compensate the lack of Catherine and Cyril at least. It would have been hilarious if his apology to Manuela was actually a support conversation
Admittedly, my death knight died attacking Rhea in chapter 12, but it is SUPER odd that you don't get him as a new character post-timeskip in Edel's route.
I suppose it's because he's a member of TWSITD, but even so.