FWIW: indeed, sequentiality is an absolutely crucial resource for making sense of ordinary conversation. There is even a well established research approach in sociology that builds on exactly that. But (!) this strong connection between turns applies to informal conversation. Things get much more complicated in more formal settings where turn-taking is organized differently, e.g. in a brainstorming session, consecutive turns are not heard as responses to preceding turns.
So I’d say it doesn’t quite work to transfer this principle of ordinary conversation to discussion forums. Indeed, one of the great advantages of forums compared to “real” conversation is that there is no obligation to respond to the immediately preceding turn (post) as there is in ordinary conversation, because this entails that people don’t have to wait for the right moment where their contribution fits in sequentially. (Of course, that also introduces new problems, but that’s another issue.)
So, if there is no necessary connection between two consecutive posts, how/when does their adjacent position matter when we make sense of their content? I’d suggest something like this: if there are no other clues regarding who/what is being referred to, we assume that it is the preceding turn.
If that is true, then there are two potential sources of confusion in the default configuration of discourse:
- If there are references (e.g. quotes) to other posts, but the post is intended to (also) respond to the preceding post, it is unlikely to be understood as such.
- Since a reply to topic also lacks any reply indicator, they are indistinguishable from a reply to previous post.