To be honest though, I can almost see Elektra as a romantic match for Frank. Both are killing machines and Frank....well Frank lives for the kill there is no doubt about that, adrenaline junkie not withstanding.
From a tactical standpoint, I could almost see Frank feeling that one day he will truly be dead, no blood stones, no agents of heaven, and NO Frankencastle. Perhaps, just perhaps he may come to feel that he would need heirs to keep the war going. Between Elektra and Frank, those would be some very dangerous heirs to the name: PUNISHER.
Say that word 'romance' over and over again. Think of all the things you associate with it, then think of Frank Castle.
For me the words 'romance' and 'Frank Castle' cant even appear in the same sentance. I mean, what would they do? What would they say to each other? Elektra at least has some evidence of being a normal person capible of having normal human feelings, but Frank is entirely incapible of that kind of involvement with another person.
As for a kid - another reoccurring theme about Frank is that he knows that he is technically the bad guy, and a monster, and traditionally he has always advocated not following the path he walks to people he would consider 'good'. I honestly cant imagine Frank ever raising a child to be a killer, it just doesnt fit on any level.