There seems to be a general consensus that we have plenty of tags on SO, and I frequently see some to be cleaned up. A script was recently introduced to eliminate single-use tags after 6 months. More amazingly (to me at least), there's been considerable effort on a tag synonym repository in mere anticipation of a synonym feature.
Would increasing the create-new-tag threshold be another step in the right direction?
How does 4,000 (up from the current 250) to create a new tag sound? It fills part of the void between 3k and 10k, but it feels about right to me. My second choice would be 2k (the same as the edit threshold). However, both are higher than the 500 required to edit tags, which should lead to more users getting experience in tagging before they can create new tags.
For a young or rapidly evolving site, this would not be appropriate, but I think SO has reached critical mass.
Why such a high threshold?
Threshold Users 250 21,561 500 14,115 1,000 8,301 1,500 5,499 2,000 4,328 2,500 3,378 3,000 2,771 3,500 2,305 4,000 2,008 Tags: 29,205
While 4k is based on my gut and general experience on SO, I believe going as low as 1k limits effectiveness. In an ideal world, we'd need just one user per topical area and that user would create any new relevant tags, but that ideal user is as mythical as a unicorn. In this world, we only need maybe 50-75 active users per ontology. However, many areas overlap and many of those users would be knowledgeable enough to tag in 5 or more ontologies, since you don't need to be an expert for that.
Once one of those users create a tag, any other user can use it, so this doesn't even require a tag-creator eyeball every page. Furthermore, it doesn't matter how many users the site has: the same number of tag-creators should be able to accommodate them. Much like low-rep behavior is today, users will comment on a tag they feel is appropriate but they can't add to the question. This can be a good thing: in those cases, creating a tag means someone proposed it and at least one tag-creator (at 4k, 2k, or whatever rep) agrees.
Numbers from thin air
If we estimate 40 different areas (probably a high guess for SO) and figure each needs 75 users but 50 of those are shared with four other areas, that gives 40×25 + 40/5×50 or 1,400 users. These users need to be active; so, going by these numbers, 2,008 users (4k) might be too restrictive, but 2,771 users (3k) could be enough.
The limit was increased from 100 to 250 (SO only) almost exactly one year ago.
A recent bug report is [status-declined], but I'm not sure what's being declined. (Does it just mean not-a-bug or [status-bydesign]?)