My experience was with v1.10.3.
As for the purpose of the feature, I don’t honestly know. I was compelled to try it because someone else thought it would be somehow useful. I found no benefit and only overhead by doing something special and off the normal workflow.
Since then, my module sits in our fork under src/modules, just like any other module. There are even some benefits to this approach. I could not figure out how to add new uorb topics in some out-of-tree manner, for example. It is easy to do in-tree.
I just thought I’d share about my wasted effort in case it would help you avoid such. YMMV and you may have a better use case, than I did.