Tag spam is a problem - not only in this context. And limiting the amount of tags would encourage authors to use only popular tags.
Here's a proposal that might be controversial: curators should be able to delete tags, within certain limits. For example, a curator with a higher reputation than the author would be able to delete one tag, while upvoting, in the first hour after publication.
Of course, nothing would be deleted on the blockchain, but a specially formatted comment would be added so that the front-end would ignore this tag.
Is this censorship? I don't think so. Tags don't belong exclusively to the post or the author. They form a link to other posts, so others should have a say.