I add in a HIIT circuit to nearly every workout. It would be awesome to be able to build that in without having to add a separate workout!

This is a must!

This! Especially for conditioning at the end of the workout - having to add additional workouts is a pain!

I often have to build a part a and a part b workout for the same day. Should be able to build a circuit and thenot a regular workout in same workout without part a and b separate

Adding in a Tabata option too

Agreed. I always include a dynamic warmup, and it would be nice to have a clear differentiator within the same workout, especially for clients that are new to working out. Maybe including the capability to add a "warm-up" section to any workout??

You practically can when you add in super sets, etc. of multiple exercises in... Otherwise, Whats the difference?

I do this all the time and it would be very helpful and it would add a lot of quality to every session

The different kinds of workouts (i.e. regular, circuit and interval) could be beneficial to have the ability to add them within the same session.
The reason for this is because I like to have clients go through somewhat of a warm-up before doing something like a circuit or intervals and it means creating two separate workouts for the same day.

I like using intervals straight after a couple of strength excersises. At an inteval workout you can only use intervals. I would like it if there was a way to combine them.