Thanks for voting and commenting on this issue.
This capability is now available using the new "Create project with shared configuration" feature, which was released to all versions of JIRA at the beginning of October 2015 (JIRA 7.0). When creating a new project, simply click the "Create with shared configuration" link in the bottom-left corner of the dialog, choose an existing project, and a new project will be creating that shares the same workflow scheme (and other schemes) of the existing project. More documentation is available here.
We recognize that this is not exactly the same as setting a workflow scheme as "default". Simplifying project setup, configuration, and maintenance is one of the JIRA team's top priorities right now. We are in the early stages of a big investment in making it easier to get started with a JIRA project and maintain a large number of projects at scale.
We will continue to work in this area and intend to provide more comprehensive support for this in the future.
It's important to understand that we rarely try to implement individual features from jira.atlassian.com, but instead take a holistic look at the problem and use feedback from the comments here and a dozen other sources of customer input to solve the core problems.
Please don't hesitate to contact me if you have any questions or feedback.
Product Manager, JIRA Platform