Jeez, just don't force them (devs) to anything, that's the worst aproach. If dev writes a character and at some point feels it should be romanced, by no means, let him do it. If you feel it's right/natural for particular situation/characters, I don't see any problem. What I'm trying to say is that in regards of writing nothing good would come from conceptual "regulations". "There has to be something/doesn't have to be something without any further thinking" aproach is the best way to screw up something possibly unique...