I am all for abolishing meta tags, but... it's not a meta tag.
Manufacturer tags are currently being used for tagging questions about machines that are obscure enough to not have their own tags. The interfaces tag could be used in a similar way - for questions about obscure interfaces that do not have their own tag. That way, if and when individual interfaces become popular enough to have their own tag, these questions will already be tagged with interfaces.
In its current use in What interface did Video Backup System use?, it is being used in a similar way to I have described, except asking for identification of an interface instead of asking about an interface that does not (yet?) warrant a tag. This usage is certainly not that of a meta tag.
(As an aside, I think that the singular interface is more consistent with existing general tags.)