That said, a ticketing system should ostensibly offer this same effect, but in my experience they're often populated with brief titles and maybe a short paragraph on expectations.
In other cases, it can be very tactical. I think you are right, probably it can be expressed directly in the form of a ticket. The discussion well happen in the comments to the ticket in this case.
Anything that will prompt stakeholders to engage and clarify expectations is a win. It's hard to make this happen even when everybody is philosophically aligned on the need to do so, so reframing it as an RFC could be quite the useful "One Weird Trick" ;-).
If the ticketing system were private to the engineers, it probably would serve the same purpose. But inevitably ticketing systems have wider visibility, and become a mechanism for signalling progress to management/product/sales... at which point engineers are actively incentivised not to put actual data in the ticketing system
or worse, multiple bulleted paragraphs fulls of expectations that have little to do with how the software actually work and is used by the actual users.