Hi everyone! I just spoke with our Academy team about this. While I was initially excited about the idea of providing an option for this, they've informed me that the reason no similar cohort exists at this time is that L3 is designed to be completed fully independently. It is used in place of a certification exam for the Solution Architect certification, and completing it independently is part of the terms of the course. At that point, we cannot support collaborative conversation around the course in the Community. However, you can find some discussions in the Academy forums tagged with the Level 3 Model Builder label.