The keyword nodelet was probably added with that in mind, but as it stands, it isn't particularly useful for much other than as a way to anonymously add words to nodes, often insulting ones. Thankfully, it is mostly ignored so far.
For it to be less abused, it would need to be subject to moderation (make adding keywords a level power, show who added each keyword, and allow voting on keywords). However, I doubt keywords would become verywhere1 enough that they'd become very useful.
Therefore, I think the best thing to do with the keyword nodelet is to delete it. But if someone wants to enhance keywords as described, then I'll add searching based on them and we can see if any keywords become useful. (:
1 Update: I replaced "ubiquitous" since "ubiquitous enough" probably bothers some pedants. I replaced it with "verywhere" which is like "everywhere" but not quite as much. Thanks to diotalevi for (accidentally, I think) coining this useful word.