I don't have strong opinions about allowing time-limited cosmetics in adventure available for a price later on. They already made some almost identical versions and I'm fine with that, even glad so I can feel free to use my stuff without having to disappoint others when they ask how to get it. I do understand the sentiment for why some things should remain exclusive, especially because they reward you for sticking with the game for so long, grinding the events as they were originally introduced, and tolerating all the criticisms of the game, bugs, and long waiting times in between content.
For this reason, I don't push for these cosmetics to become available once again, but I also wouldn't oppose Rare if they decided to do this, or oppose anyone who asks for this. I would really like there to be a reason to use doubloons so that these can actually have economy around them. It is just a matter of whether it is the best way to make doubloons useful and whether it is worth development time. There are exceptions though. Should the year 1 pirate legend rewards be available for everyone? Probably not. But other cosmetics I don't even remember doing anything to earn and so I don't have any reason to be possessive of them.
That being said, I am a strong advocate of making twitch drops available later at a cost, except I believe this should cost ancient coins personally. Rare should profit off of these, and it is a missed revenue opportunity on top of the value they already get in drawing people to twitch. I've posted before that it is possible they are forbidden, contractually, from making these available elsewhere through a kind of agreement with Twitch, as I cannot see any reason not to re-release these in the emporium 3 or so months after they initially drop.
For the inevitable naysayer, I believe it is fair to draw a distinction between things earned in game (i.e. were well advertised, available for more than 24 hours, and required true effort) and twitch drops which you can earn just by idling and only require you to either keep up with social media, check the page everyday, or just get lucky. I think there is some degree of work put into staying on top of these, but not to the point where they should be exclusive and gone forever. That is why they should be available only for ancient coins, but at a reasonable price, something like 50 ancient coin for each piece. This would allow most people to buy pieces they are missing, or sets they want without making them commonplace.