We've decided to update XKit. It's harder than it looks. We're not in contact with the original XKit Guy, nor do we have access to xkit.info. We currently operate at this blog and on GitHub.
Would it be possible eventually to have something that'll let you tell tumblr to forget you ever used a tag? So that it doesn't persistently suggest ones that have been replaced/accidental misspellings/etc.?
Good idea! I’ve made an issue to suggest this and perhaps someone will be making this.