Where I live at least, legal marriage is essentially a contract between a man and a woman to have children, that is, to give them a full legal name and assume a series of mutual responsibilities that revolve around the kids' raising, including mutual fidelity and the administration of wealth. Further rights, such as women's alimony in the case of divorce, are founded in the notion of child support as well and within our patriarchal society; in the last few years, gay legal marriage was approved in some cities of my country under the assumption of extending a similar economical society between gay couples (I have no idea how they decide who the functional "man" and the "woman" are there, especially if both of them have an income), followed by an initiative to legalize and regulate their adopting of children...
So, as you see, either traditional or gay marriage is based on the concept of couples as social agents of human biological reproduction, so no legal marriage with fictional/synthetic characters of any sort has any foundation yet.
Also, notice that no mention of love took place in the matter. The alleged equivalence between the institution of marriage and love, if existent at all, duels not at a legal but merely religious/moral level: you're not obliged (nor expected, before modernity) to love your legal partner. So I, openly antinatalist and posthumanist, see 2D love as an escape from all this farce of conjugal happiness and the salvage of true love (for what that would be there are other threads around and in the archive), and so I have no wish for my waifu and my choice to be absorbed by their poor excuses of social institutions.