A lot of my opinion on this is informed by my experience in early-days Ruby and C++ with viable templates. It has the feel of the kinds of magic that I came to find very frustrating in both those languages.
The other thing is that fairly frequently my goal with collect isn't really to collect anything but to stop processing on an error. Sometimes I need to do this on a couple of layers and the intermediate vecs are gratuitous storage.
So my actual proposal would be more like having a simplified version of `scan` that's specifically for iters of results and then it's two steps: process-until-completion-or-error and eventually down the line collect-into-container if I actually want that.
Specifically, the weirdness here is that FromIterator<Result> is an implicit conversion between apple-and-oranges container types. Which is quite unlike most (or even all) other FromIterators and it has a complicated type relationship that makes everything else just slightly worse just to give people an ooh-ahh moment when rust does something they don't understand but is helpful.