From what I've gathered skimming the numerous blog posts venting about submodules, it seems that people have trouble with submodules because they are trying to integrate them into a workflow they work poorly in (i.e., rapidly changing modules). There seems to be room for improvement for that type of usage, given what people are saying, but I wonder if there have been any changes to submodules since those posts (many of them are dated around 2011-2012).
My own positive experience with submodules involves dependencies that only occasionally change; I can always point to a specific tag that should be used.
Even if the interface is stabilized, when you update implementation of a submodule you will still have to recursively update all submodules from main down to the changed module.
