Well, time to throw some more raw meat into the gladiator and tiger pit.
Dimitri x Ingrid
Ingrid really goes well with most, if not all, of the Blue Lions boys, but I can't be the only one who sees how good of a queen she'd make. She's fierce when she needs to be and can be soft and caring, dare I say motherly. She could easily do what Byleth did for Dimitri in his route with the cute comfort and "You're alright, you've got this" stuff.
Hubert x Edelgard
There could be some social hurdles to jump through for this one. But I see it working because Edelgard isn't going to live forever, especially with her crest implant shortening her lifespan. She'll need to make an heir to take over. She can make Hubert her prince consort and nobody would have the right to complain too much. There's already a strong bond there. Might as well boink the guy who's least likely to turn around and backstab.
My Claude ship is with Hilda, but I think that pairing is done a lot so it doesn't count as underrated.