I don't know why everyone is upset with this. Lydia wasn't marriage material on first release, but a patch sorted that out... Why anyone would want to marry Lydia is beyond me, she's a pain in the arse...
Indeed. But here's the difference between her and Serana:
Lydia: No dialogue for marriage, which appeared to be a glitch considering guides claimed she WAS an option. Later patch fixed this. She has next-to-no story, personality, or anything beyond being the easiest bit-I mean "housecarl" a player can get via main quest
Serana: Actually HAS dialogue explaining WHY she can't marry you, so it's obviously NOT a glitch. Actually has a deeper story and personality than pretty much every other character in the game.
The only way marriage to Serana would work is if a patch gave you a dialogue option to suggest getting married outside of a hold capital in some isolated house or landmark by someone other than that priest of Mara...Hm...I wonder how a marriage performed by Florentius would go XD Hakron...would probably not be as fun D=
Well, that's highly unlikely and I highly doubt Bethesda will ever make Serana a marriage candidate, so I would just take my advice and suck it up; deal with the fact that not everyone will marry you =3