Thanks, actually haven't checked that subreddit in a while.
I've seen many people suggesting that Shamrock played a role in Kidd’s youth, obviously as a negative figure. That is certainly possible.
However, obviously now we know Shanks, the real, Shanks potentially dealt Kidd, his biggest losses. His arm, destruction of his crew and also destruction of the Victoria Punk ship(Interestingly Toei added a scene of him caressing his ship before the incident with Shanks - a very rare scene of kidd considering we always see him high octane and ready to go fight anyone. Clearly Victoria and his ship Victoria Punk had immense meaning to him.)
I think when he returns Shanks will be the number one thing one his mind. And it is also possible he may learn about Shamrocks, and if Shamrock was the one who did those terrible acts when he was younger, hey may try to go after him as well. So possibly both...
And also, those were two Incidents with Shanks/Crew, I 100% believe there will be a third. Third time is the charm 😉
There is a recent longer youtube video done by DawnDuskJapan. It's on the connection between Kidd/Rocks. It takes a slighty different angle than the theory you've linked above. Imo probably the best theory vid I've seen about Captain Kidd on YouTube ever.
And there are also a few other vids done other creators recently on this topic.