The devs already said that dating multiple people at once is out of the question, or rather, an impossibility. I wouldn't expect it to be implemented in the future, if at all.
Okay, before this dives into another intense argument, ShroudedLion is right. We won't be adding poly. We aren't confident enough that we could write poly and it would be an injustice if we made it only for the reason of "two is better than one", cause that is not the main essence of a Poly.
Also can you imagine how much work that would be? I'd have to write 30 different scenarios for it to fit... I love working on this game, but I don't want to milk it dry...