tbh, I hope this doesn't sound rude but Edelgrid could have been like a half-joking suggestion that seems to have slip through but I am all for it though especially when Ingrid is notable for supporting the three other male lords but not Edelgard.
Ingrid is unfortunately one of the most aggressively straight characters in that game but the one paralogue with her and Dorothea and their supports has always fuel and endless amount of yuri between them.