I figure BAIN users are probably mod-savy enough to figure out the manual edits to my config files themselves, without the benefit of my install scripts to guide them.
BAIN doesn't have scripting support, and that's OK as far as I'm concerned since very few mods really need it, and I don't mind (actually prefer) editing config files myself.
BAIN "support" in a mod means archiving it with a directory structure that BAIN understands. Most mods fit BAIN's definition of a "simple" archive, with all the content (.esp/.esm, Textures and Meshes dirs, etc.) sitting in the root of the archive or a single subdirectory. Some mods come with unnecessary levels of directories inside the .zip (e.g. "Program Files\Oblivion\Data") and those can't be used with BAIN unless the user manually repacks them.
http://tesnexus.com/downloads/file.php?id=3409 is a good example of what I'd call a well-made mod archive. Everything's in the root so BAIN users can install it easily, it has omod conversion data for OBMM users, and it's straightforward and understandable to people who use neither tool and want to install manually.
BAIN also recognizes what it calls a "complex" archive format, with subdirectories for groups of files that can optionally be installed or not, independently of each other. Most mods don't need that; Cobl is a good example of one that does.