hey, don't apologize, i'm so happy you came back to clarify!! and sure i'd love to talk about this, but i don't think there was a "plan" in the way that you're thinking of it.
i think, genuinely, that it was some sort of miracle that ned was tasked to take theon to ward in the first place. the greyjoy rebellion was 9 years before the start of agot. robert's rebellion was 15 years before the start of agot. so we're six years into a new regime that was started in a pool of infant blood. robert baratheon HIMSELF was there to rock balon's shit.
acok; chapter 11, theon i
and we know how merciful robert was to his enemies... like he's so fresh off the high of killing rhaegar and elia and their tiny, terrified children you know he's jonesing for another greathouse to wipe off the face of planetos forever.
so it's shocking to me that theon was permitted to live at all. i think that was a tense and angry conversation between ned and robert and i think it was decided because ned threw in the ol' "your reign was begun on the mangled corpses of babes" line. but maybe i'm wrong and robert had no real feelings about keeping theon alive or not, especially considering the fact that rodrik and maron were casualties of war. they were not purposefully executed for their or their father's crimes.
acok; chapter 11, theon i
so, maybe i'm wrong about robert and ned's marital spat over this. we don't need to get distracted over that at this point, i don't think it really matters.
i think it's sort of impossible to say what the intent of theon's captivity was because we get nothing from ned's perspective on it. and he would know best!
theon is not a reliable narrator here. he describes ned as "cold", but this is the ned who brought him along with his trueborn children to see justice done in the northern way. who fed and clothed him and ensured that he was treated as befit a boy of his station, as an heir to pyke. theon describes cat as "even more distant and suspicious" which is crazy because cat planned the entire royal visit to winterfell with theon and robb sharing equally in all the activities of the king's party and then permitted theon into her confidence in her sick room after the attempt on bran's life. she raises some moderate reservations in response to her 15 year old son about putting their 19 year old hostage in command of his war host.
but it wouldn't be fair of theon to be a reliable narrator, here. he was kidnapped as a child and a headsman's axe was hung over his proverbial neck for nine years. he isn't going to be an objective judge of cat and ned's behavior towards him because regardless of where he was seated during dinner he was still their war trophy. because regardless of how gently cat and ned treated him he was still their political prisoner. and that's not a dynamic that's washed away with family bonding activities and a lord's wardrobe.
importantly, though, cat is also not a reliable narrator wrt theon's captivity. i have a tag on my blog about the two of them and about how cat evaluates theon's place within her own household. i've been paying close attention to that in my current reread and so far i can't quite put my finger on it (though i suspect cat sees theon as just a normal ward like how petyr was her own father's ward and how ned was jon arryn's ward etc. until war begins to brew and she remembers that theon is, in fact, representative of a potential and proven adversary) i fear that now that i'm past agot i'm not going to get very good information on how cat stark sees theon greyjoy because he is very quickly going to change from her husband's ward to the boy who murdered her two youngest children and burned winterfell to the ground. and she can't really be objective about that either.
but we know this from maester luwin:
acok; chapter 46, bran vi
and i think this is an accurate summation of the "plan" wrt theon. theon was the only surviving heir to pyke. he was raised for the first ten years of his life as a third son and a youngest child. he would never have had any thoughts of succession or inheritance or rule (by mainland standards). ned felt confident that he could rehabilitate him into a good upstanding northerner and rid him of his cruel ironborn blood.
but this is a whole lot of build up without me really answering your question. i tend to waffle.
anyway. i do literally think the plan was to play it by ear.
i think ned told robert that he could rehabilitate theon, the heir to pyke, and turn him into an upstanding mainlander just like jon arryn turned them (ned and robert) into upstanding... vale. ians. and i think the plan was absolutely to keep theon stuck in a labeled tupperware container at winterfell until balon died and then to ship him back off to the iron islands to run them like an upstanding mainlander would.
i do not think that ned nor robert spent any time at all thinking about ironborn culture because ned and robert just see ironborn culture as "those savage pillaging rapists from that shitty little chain of islands out west". i do not think either of them ever thought "huh. perhaps the ironmen would not accept an heir to the seastone chair who was raised off of the islands by outsiders and turned into an outsider by his captors". i think ned and robert both thought "if the ironmen do not accept theon as their liege lord when we give him back in 20 years or so we will come back here with our scorpions and our catapults and our big fuckass warhammer and we will beat them into submission again, because it was pretty easy the first time tbh these guys are jokes."
and i think it wouldn't have been too too wild for them to think this if the whole like, plot of the series didn't happen. robert's reign isn't very destabilized. he clearly is in possession of like intense military prowess. if euron or victarion or aeron said when theon was brought to pyke for balon's funeral and to take his place as the liege lord of the iron islands "hey, fuck you guys, that's not how we do things here" i think ned would not have to try too hard to remind them how it went the last time they tried to assert ironborn independence.
so, yes, to us, shipping a fully grown theon off to pyke to assume the lordship over the islands seems guaranteed to go poorly. but we have perspective into ironborn culture that ned and robert do not. and we also, like. care. about ironborn culture. and why the iron islands do things differently than mainland westeros. and why they would reject theon as an outsider as soon as they looked at him. ned and robert do not care about these things. their plan was to go in and put the little puppet they conversion therapied into a wolfbrained greenlander onto the seastone chair and tell everyone on the islands that they would squash them like the useless bunch of roaches they are if they don't accept his rule. ¯\_(ツ)_/¯
