The Appointment Group function needs to have features that make it work more effectively in the classroom context. Namely, instructors should be able to rename the time slots to allow to create topic sign up sheets, not just time slot sign up.
Voted! Meena K, at our institution, designers help instructors with that need by editing the Description of individual appointments. While that works pretty well, I do like your idea of renaming the appointments to show distinct titles for topics.
Also related to M. V. Ramana's comment: In many courses, we use self sign-up groups in a group set for group project topic signups. With the Groups tool in People, it's easy to rename a group to match the topic -- or even assign a student leader to a group and have them fill in the topic as part of the group name. See my GROUPIES: Group Assignments video for lots of tips on self sign-up groups in a course.
The idea is to use Canvas to have students sign up for group projects on one of a chosen set of, say 10 or 20, topics. That way all those who signed up for a topic would be assigned to a single group.