It's no secret that I think plugins are unnecessary. Unfortunately, they are also popular, largely due to to how easy it is to create a plugin and put it in your Rails project.
It's also easy to create a new gem. In 2006 Dr. Nic released the newgem gem. This was a great step in 2006, but it's 2008 now and it doesn't feel like we've moved much in the way of shared ruby code.
We're all to blame.
The vast majority of Ruby work is working with Rails. I do believe the next step for RubyGems is to play seamlessly with Rails. Since RubyGems are great for any Ruby code, it doesn't make sense to add Rails specifics to RubyGems. However, RubyGems could be more opinionated about how gems are structured. Right now, RubyGems library code can be structured in almost any way that you'd like. If the structure followed a stricter convention then auto gem loading code could be written for Rails.
I like newgem, but I think the features provided by newgem should actually be part of RubyGems itself. If the gem command could create a project skeleton it could be opinionated about the file structure without creating a larger barrier to entry.
There is another change that needs to happen. Everyone knows that you should vendor everything for your Rails projects. But, there's no single step to go from uninstalled gem to vendored gem. The path is generally to install it locally and them unpack it in whatever folder you've created that gets autoloaded.
I'm pretty sure a remote unpack is fairly simple, which is why we are all to blame. RubyGems is an open source project. Anyone can contribute patches to make it better.
Lastly, if gems become the standard way to share Ruby/Rails code then we'll need a few rake tasks added to Rails. For example, who wouldn't want a rake command to upgrade to a later version of a gem.
I'm hoping 2008 is the year that shared ruby code becomes synonymous with RubyGems and the year Rails Plugins become unnecessary.