Intersting!
I would also add that Task name is not unique and you can use to describe the "process / goal etc" which would make it pretty obvious to search / review from the UI.
Regrading models and branchs, Iw ould use the Task tags (you can have as many as you like) to tag the specific model type (or dev branch if the alg is diff), this means you can also easily filter based on the Tags in the UI.

can you use the Web UI to compare the artifacts from two separate subprojects?

Yes comparison is not limited, in the comparison mode you can add any Task to the comparison, you can also have "flatten view" of projects (i.e. Tasks from all the subprojects) for easy access