It looks that becoming a partner costs $10k per year.
We wanted to create a free plug-in first, but already with the support for the enterprise edition. The plug-in is going to be integrated into magento checkout. It is basically a widget. when you click a link - it opens a popup and helps people to ship internationally. As a next phase we were going to make more complex integration where the support of enterprise is a must have as we already have few potential customers with enterprise edition.
Is there a way at least to test plug-in on the demo version of enterprise edition? http://www.magentocommerce.com/demo/enterprise-edition-request
And what about the differences between community and enterprise version inside the code in the checkout process? Do they have something in common?