So basically you want to bookmark replays with a comment?
We could add a "bookmark for later" flag to game reviews in the database. In reviews you can already rate and comment a game. And then the client needs a feature, to show/sort/edit your bookmarked reviews.
This is technically possible, but seems like a very special use case with a very very small audience. Calling out @MarcSpector whether you're interested in adding such a feature.