Like it.
I don't see a way to add a subevent. This seems a little scary. What happens when we have an entire complicated event setup and the organization decides to add one more session? I hope we don't have to start over.
I'm wondering about the order of the three options.
Seems like #1 should be the simplest: Single day with no subevent
#2 should be second most complicated: Single day with subevents
#3 Multiple day event with no subevents
What happened to #4 Multiple day with subevents?