Both answers on the question Should questions always be tagged with either a console/platform or with “multi-platform”? make perfect sense to me, i.e. on the one hand this might overuse the tagging system but on the other hand it would help a lot for filtering.
Therefore I suggest a system which, in this case, would internally store the platforms to which a tag is relevant and
- if a question is tagged with one of these platforms, nothing special will happen and the question is to be considered platform specific (e.g. a bug which only appears on the PS3 version)
if the question is not tagged with a platform, the only result will be that the tag filter mechanism works a bit different compared to what would happen if the question was (invisibly) tagged with all platform tags:
- If the invisible tagging is definite on interesting or ignore (i.e. there is not at least one ignored and one interesting tag) the usual mechanism works.
- if the tagging is ambiguous (i.e. contains both interesting and ignored tags), no filtering happens at all
The actually attributed tags must of course override this behaviour. That way questions about a game one likes but which is available for a platform one doesn't care about will still be highlighted unless specifically tagged with that platform, but no additional tags have to be used to filter a game which is only available on ignored platforms.
I am only unsure whether search should include those hidden tags, too.