It would be nice but I don't see it being included any time soon.
Couple ideas I've seen people use to solve this:
a) Use product types to organize your collections, then add tags for sub collections.
b) Use Bulk Edit Tags and take the approach of adding tags to products for a collection (rather than excluding tags).
Hey there, you can try using our app Advanced Collections - https://apps.shopify.com/advanced-custom-collections - to create collections which exclude product tags. What is created is just a normal manual Shopify collection which the app sync periodically according to the conditions chosen, and you can use it in the Shopify admin for various purposes e.g. for discount codes. There is a 7-day free trial to try it out. Hope this helps!