Well, what I really meant by "it becomes apparent that most of the complication is necessary" is that signature ascription packages up a bunch of things (hiding labels, making types abstract or not, um, some others?) which programmers feel are related into one construct, but they are actually different and so things get complicated.

Is there a technical good reason functor application should be generative? I've been using OCaml for a while, and applicative functors feel very natural. (ETA: there are some weird corner cases where proving that the types that result from two different applications of the same functor are the same fails for mysterious reasons, though. I *think* I once found a mailing list post by Xavier mentioning that there was a better way to do this than they did, but I do not remember the details and I think it was unclear to me at the time.)