I think this would work well for the types of collection assets that we'd likely use it for. What I've done is this:

Greitens coverage -- https://www.stltoday.com/news/local/govt-and-politics/post-dispatch-coverage-of-greitens-his-campaign-and-the-mission/collection_1f91d9e4-20fe-5c4d-9f53-dd661198f3ec.html

Crooked county executive coverage -- https://www.stltoday.com/news/local/govt-and-politics/st-louis-county-executive-steve-stenger-pleaded-guilty-to-pay/collection_9b20ca96-c708-594d-9504-1beabb91170f.html

Which I'm doing by adding link assets to a collection set to "series" presentation. Then I add it as an embedded gallery at the bottom of relevant articles, and it acts as a topic-specific "infinite scrolls" of sorts. 

Having a collection that auto-populates will eliminate one of the steps in that process. I'd probably still create link assets for relevant articles, as adding a series collection as an asset (embedded or not, if I remember right) to an article/collection/asset that is in the series causes the site to crash.

But even for photo collections on ongoing issues (floods/major news events), this would be great to auto-update the collection as assets hit the system.

Yes, this would be amazing. -- by keyword would work better for me than by slugs (and keywords can be batch edited; I don't think slugs can)

Yes, exactly.