Links to Relevant Wiki Articles(s):
The best place to post ideas for Scratch is on the Suggestions discussion forum. That way lots of community members can help think through your idea.
http://scratch.mit.edu/discuss/1/
Remember -- it's best to post one suggestion at a time. That way everyone can contribute their thoughts on how to improve it. And it's always good to make a Scratch project "mockup" that demonstrates how your new feature will look and work.