Tags are driven by questions, not the other way round. So if there is enough demand for a tag we can create it. But there isn't much point creating tags first and then waiting until they are populated.
Do you have a feel for how many questions require this tag? Can you post links to them?
I'm not sure I agree that sound-design isn't a useful tag. It's more that the site is horribly named as we cover way WAY more than just sound design. cable and cables should probably be merged though.
Cables has been merged with cable. Sound-design will not be getting removed at this time as it provides meaningful categorization.
Personally, I have no objection to either approach. I think either can be useful, however I think it is noteworthy that even major tags on SO have not been redone under the type B approach, so it doesn't seem that reworking as the second type is something we "need" to do.
We've been using case A and I don't really see any strong need to switch to B as I ...