Curious. I teach a second year undergraduate class in Australia, in which I put the whole class onto a single codebase, typically growing it from 1,500 lines at the start to usually around 60,000 lines by the end of term. (Possibly slightly less this term -- I've moved universities from UQ to UNE and it's a smaller class this time around)

I haven't noticed students hitting a wall in that process -- the code isn't always very good (they're students) but the groups generally get there with the code, and struggle instead with large merges, group dynamics, writing tests, etc.

This could be because I've already put the general architecture and build system in place before they start, but I wonder if there might be something else at play too.

(Well, or maybe they are hitting the wall, but as they need to do this to get through the unit, they scrabble frantically over the top of it...)