Plugins really are unnecessary — Jay Fields is absolutely right. RubyGems is a great package management system and there’s no reason it can’t do double duty here, if we just impose a few extra restrictions on Gem/Plugin structure. There are other benefits too using Gems too, such as versioning and dependency management, which is somewhat painful in the world of Rails plugins.
Merb already uses Gems for plugins/extensions. Why doesn’t Rails? Historic reasons, most likely. Rails itself predates the existence of Gems iirc. But seriously, how hard would it be to rewrite `script/plugin` to install a gem and unpack it into `vendor`? That’s the first step.