@kaniini im not sure that addresses the problem. If you dont have consistency in the keywords then you cant create sane rules to take advantage of it.
@kaniini im not sure i agree, its the same reason the hash tag system isnt effective at creating topic-based lists. On any one topic there are dozens of iterations of hash tags used to describe it. So the system doesnt work too well. I dont think the solution is viable or workable without some tweaks. But could be made workable with the right considerations.
@kaniini I have been giving a lot of thought on how to do sub-threads correctly as well. I think both problems are very similar. I just dont think either will work if you keep the keywords free form without some mechanism to create congruity.
that's why you allow recipients to choose their own rules for filtering on.