And this is the vibe I've always gotten, especially with Lyanna. If we take Arya as a template, and who in all actuality was raised more gently than Lyanna would have been, Arya would be VERY hard to get and keep, as I think she might turn to anger to deal with her embattled feelings.
So too Lyanna I think.
More to your point, another quote from GRRM on marriage and how this might relate to Lyanna:
“And then there are some things that are just don’t square with history. In some sense I’m trying to respond to that. [For example] the arranged marriage, which you see constantly in the historical fiction and television show, almost always when there’s an arranged marriage, the girl doesn’t want it and rejects it and she runs off with the stable boy instead. This never fucking happened. It just didn’t. There were thousands, tens of thousand, perhaps hundreds of thousands of arranged marriages in the nobility through the years of the Middle Ages and people went through with them. That’s how you did it. It wasn’t questioned.” - GRRM by James Poniewozik, Time April 18, 2012
I completely agree with all the above. I have always thought their relationship would be fraught with guilt and inner conflict, and I could totally see Lyanna trying angrily to resist it, knowing what she knows, that there can be no hope for them.
As for plans, I know I've never made plans that have turned out as I expected- ever.
In terms of Martin's use of "irony" and fate, (and I do think they were fated), I always speculated that Lyanna and Rhaegar just missed one another when he wasn't married, which makes all the " if only" claims by Viserys, Dany,Cersei, and Kevan even more, well, ironic.
After not finding a suitable dragon girl, and before the ruling lady of Dorne one-upped Tywin when he turned down her children, I wonder if they planned to look around the kingdom for his bride, purely speculating of course.
“The battle between good and evil is a theme of much of fantasy. But I think the battle between good and evil is thought largely within the individual human heart, by the decisions that we make. “It’s not like evil dresses up in black clothing and you know, they’re really ugly. These are some of the things that Tolkien did; he made them work fabulously, but in the hands of his imitators, they become total clichés. I mean the orc-like creatures who always do dress in black and … they’re really ugly and they’ve got facial deformities or something. You can tell that if somebody’s ugly, he must be evil. And then Tolkien’s heroes are all very attractive people and all that, of course, again this become cliché in the hands of the Tolkien imitators.” –GRRM by James Poniewozik, Time April 18, 2012