This was an old idea and I finally found enough toits to finish it. Basically besides normal key words searching, one can use a tag cloud to help find alternatives. Here are some examples:
By clicking on any of the links in the cloud the keyword/tag is added to the search string. On the top there are "+" and "-" that can be selected before selecting a tag. The selected "+" or "-" will be added in front of the keyword to force inclusion of exclusion of a keyword in the search result documents.
Only time and some usage will tell if it will be useful or not. Let's see.