Is there a plan of making UltraNavigationBar for WPF?
Sorry, I don't know exactly...you should contact Developer Support. As long as you have purchased NetAdvantage, it doesn't cost anything - we welcome any constructive feedback we can get.
how can I sign up for a beta participation? how much does it costs?
As a matter of policy we cannot comment on future releases, but if you sign up as a beta participant you get an early preview of new features.