The patch glitches has always been unreliable for future character inclusions, but it's mostly because the bugs are often quite vague mechanically and oddly character specific. This one seems pretty clearly about mechanics and not character specific, plus the "new" mechanic here is quite specific and make sense as a possible game design idea. There are already a few examples of special dashes, like the inkling one, and such concepts are similar to special dodge like Bayonetta or Mythra, it's really easy to imagine this special dash actually happening. Now what's more intriguing is how perfectly fitting it is for Touhou representation and I don't see anything else that would be represented as well by this concept.
But I'm wondering why this glitches keeps happening, there definitely has been several cases of foreshadowing glitches, and maybe some others that we didn't catch or understand. It bugs me because it doesn't make sense from a developer point of view, developer is my job and we definitely don't ship unfinished stuff in the live version, there is a programming tool called "branches" that's made for that, so that you can work on different features at the same time without affecting other features or developers. So there is no reason for this to happen so regularly unless it's intentional.
There might be a reason to do this intentionally but I think it's a bit lazy : When they need to add some new mechanics to the game that's shared with several or all characters or that reuse/modify existing mechanics, maybe they rework the shared part and ship it live just to detect if it breaks already existing content. In general, testing old content to check for regressions is very costly, especially for big projects, that's why such bugs happen quite a lot in general. So they might want to use us players to find those pesky bugs, then there are able to develop the new content on a good code base, preventing bugs when the new content eventually release. In the end, it's the same bugs, but it's much less noticeable when it's old content rather than new content. It could be considered a lazy pratice, but at the same time it shows quite good long term planning.