Might be a bit late for the topic, but I was struggling with tags when i came across a new app in the marketplace called "Remove All Tags". It simply allows you to do what you expect it to do. You can actually put exceptions. I leave a screenshot here in case might be useful for any of you. From now on, i don't need to worry to update my workflows when a new tag is added.

I even had the chance to talk to the developer and explained me there are more apps coming for these kind of things

Workflow 'remove all tags' condition' 100%

Yes, add a workflow action "Remove All Tags". This will be helpful and save a lot of time when creating certain scenarios when adding and removing tags on recurring triggers OR when there are 50 tags to a contact. And a "Remove All Tags Except"... this allows you to remove all tags except the list you provide. This eliminates the headache of having to select every single tag to remove given different conditions or triggers OR having to add back in a list of tags that are still intended.

I agree, please add a trigger action to "remove all tags"