So it seems the 'technical limitation' was not one inherent in EA's account management system and needs to be overcome, but rather one that they have deliberately thrown up. I'm damned if I am making a second account, that kind of thing really grates me. I've said before that a bunch of duplicate accounts would serve to inflate EA's platform user numbers, maybe in this case in an insignificant way, but I am sure it looks better for EA to have an inflated number of users.
My experience with EA products goes back to LHX Attack Chopper in 1991, I've played every Battlefield Game since BF:1942, including BF:Vietnam, except BF Bad Company 1 (ironically because it was a console only launch and back then I didn't own one). I was one of the people that bought Hardline for goodness sake! The godawful state that BF4 launched in back in 2013 (https://www.eurogamer.net/articles/2014-06-19-ea-addresses-unacceptable-battlefield-4-launch) was probably the reason I decided I tried an EA product on console in the first place and had this bloody linking business come up in the first place. (If I recall it was terrible on console too - I glitched through the deck of that sinking aircraft carrier on single player one too many times and gave up in disgust)
My Origin library only tells part of the story of my relationship with EA's products. I am not making a second account to workaround some arbitrary restriction that they have placed in the system.
They could look at the age of the accounts in question, everyone here has mature accounts with lots of content on both sides and apply some judgement. I'm not trying to game the system, and I am sure that they could implement a process to weed out people who are.
The support ticket history seems obvious @thekurse , an annual or 6 monthly restriction on linking another Xbox account to your EA account, similar to unlinking is another, making the process only possible through a support agent who can verify the account activity. Nothing about this is insurmountable.