There are already pretty clear guidelines regarding self-promotion and the like on the forum:
This doesn’t really relate much to whether brand accounts should be allowed, though, and further discussion on this subject is best kept to a separate topic.
I haven’t really reached a clear conclusion on whether I think ‘brand accounts’ should or should not be banned. Perhaps it would be enough to simply strongly encourage the use of ‘individual accounts’ (as many brands already choose to use on this forum). It seems clear that some brands who would like to engage with the forum would be left unable to do so with this proposal as a hard rule.