It would be great if Lightroom came with an easy and quick way to give an option to MERGE ALL duplicate keywords. Right now I am using a hierarchy of Alphabet listing so I don't hit the limit of keywords that make them not show on the list. But that brings new problems like when one keyword is already inside one hierarchy (lets say letter A) and you have the same world outside it, you cannot drag them inside the hierarchy because the same keyword exists already there. So suddenly you have the same word in multiple places. It might be useful for some limited things, but in my case I would like to merge that keyword into one and not have them scattered in or out of my alphabet hierarchy. There is a slow a cumbersome method to solve that as explained in Lightroom Queen, but it would take weeks in my case to fix all the keywords.
Please Adobe solve all the Keywords issues that you are dragging now for years without any path.