Yes, there should be a tag. Tags are used to find questions similar to each other without having to rely on the (sometimes rather naïve) "Related" engine used by StackExchange. The obvious exceptions are the code-golf, code-challenge, fastest-code, popularity-challenge and king-of-the-hill, which are there to distinguish question types (much like the language tags on StackOverflow)
The new catalogue tag should not intend to replace these tags - as Martin Büttner pointed out, they are not fundamentally different from either of these tags. But then, is arithmetic fundamentally different from number-theory; is regular-expression fundamentally different from string? My point is that tags are in general not used to identify fundamentally different questions, but to find related questions.
This new tag should also be considered as a device to find related questions. The fact that there is a Meta post doing exactly that, shows that there is a demand for this. Why would we want a meta post, which should be linked from all included questions to easily find related questions, when there is a fully developed tags system that does exactly that?