you know who did the "One Year Only" style content correctly? Unus Annus, the filthy fleshtubers they are, which was a year of them going down a bucket list each day and filming it for the channel, then deleting everything on the last day, only leaving their memories afterward. even more, they had limited merch for each "arc", so they still made money from it at the end of the day.
if I were a chuuba going after that sort of content, or a group of chuubas making an alt-channel together, that is what I would learn from in order to see success beyond the initial "push" - if not study that era of content to better design the overall "campaign" itself.