While Spacemacs is a good project I personally prefer my own configuration.
I prefer to call Emacs «Emacs» (sometimes I even call it by its full name: Gnu/Emacs, as the elders taught me). Spacemacs is to my best knowledge some alterations to keybindings and a collection of elisp packages, put together and configured to work really nicely for many people. While I am interested in how the Spacemacs configs can improve my Emacs, it is not really “idiomatic” Emacs, and I would probably end up very confused if I tried Spacemacs; but I could see something and go «that is pretty neat, we could do that in Alchemist!»—some of the features that has been added to alchemist over the times has come from other Elixir modes and integrations: one example is the integration with the Hex package manager where information (versions, author, etc) is fetched from hex.pm and displayed in a buffer. That idea was blatantly stolen from a Vim-plugin.
We do nothing to elixir-mode and alchemist that target Spacemacs or any other starter package—it is totally neutral and non-biased in that regard, and in some cases features (such as code folding) are not even considered to be implemented at all because other elisp packages handle that better than alchemist could do, or because some people might prefer an alternative auto complete engine, or something third—so I guess my rant would end with the wish for a vanilla Emacs/Alchemist.el thread; and I’ll pop my head into the Spacemacs thread once in a while to see what’s brewing!
I don’t intent this message to be condescending. It is my hope that it is informative