For right now I found this temporary solution:

With the Plugin "CtagsInterface" I can create the following user-defined (dynamic) Action (which is a SQL-select-statement):

select tags.name,tags.file_id,tags.pattern,tags.a_line,tags.a_kind,tags.a_access,tags.a_signature,tags.a_class,right(files.file,15) as a_file,files.*,map.*,origins.* from tags,files,map,origins where tags.file_id=files.id and files.id=map.file_id and map.origin_id=origins.id and origins.name='{project}'

With executing this statement all tags of the currently (in Project Viewer) selected project are displayed in a seperate (dockable) window.

Main disadvantages:

1) The summery of the individual items in the list is pretty complex and therefore it may be hard to get the desired overview. It may get a little better, if you adjust the number 15 in "tags.a_class,right(files.file,15)" according to your needs. Unfortunately I found only a static solution for the length of the path/filename string.

2) There is no way of changing the sorting of the results in case you don't like the default sorting. (Well, I guess you could adapt the SQL-statement, but in the results-window there is no option.) In the version I got installed the Plugin at least allows to filter according line-numbers and file-names (depending on the tags-content in the DB). That's not really sorting but at least it's better than nothing.