Do you know if there are plans on open sourcing the plugin also?
There is already a open plugin based on the OpenJDK. It's called IcedTea. Look at http://iced-tea.org/wiki/Main_Page for information. Im using it on Gentoo x86_64 and it's worked very well so far, without any proprietary software needed.
@Kano: Are you reffering to IcedTea or one of the older free Java-replacements? Afaik IcedTea should be fully compatible. Maybe you'd tell us what sites you've got problems with?