I Would Like to request a tag cloud plugin

[exdiogene]

The tags are normaly typed when creating the thread first post, if you mean that its subject should be parsed to extract the possible tags from it, then if would need some artificial intelligence to choose only proper words!

Unless you are suggesting to simply extract all words longer than 3 characters and dump them in the tags box, this would need to be done using javascript, because it should be edited before the new thread is posted. Another solution for this without javascript, is to enable in AdminCP a setting adding automaticely these words in the tags when the thread is saved.