Do you think Fallout 4 will include romantic interactions? Skyrim took a pretty cool step forward in introducing marriage as a system; it was a little silly, since all you had to do was wear an amulet and do someone a random favor to raise their disposition to marry them, but it was still really awesome that you could take a spouse in the first place, and even share their home.
I'm hoping Fallout 4 expands on it a bit more, and even does romance candidates in a similar way to how New Vegas handled companions; have a smaller amount of possible partners with fleshed out personalities that you have to do a moderately sized (and romantically oriented) quest for to earn their affections.
And karma should definitely be a huge factor in whether they accept you, or even stay with you. Nothing like getting dumped for blowing up a city, am I right? Of course, the option to get a new partner or even have multiple partners (who may or may not be cool with that) should be there.