Yeah fairly impossible. Every script has a different autentication process whether it be flatfile or sql or whatever. You'd have to have a worldwide consensus of programmers to use one authentication system to be able to create a plugin to tie any two or more together. Whereas Gossamer products use one authentication process enabling a plugin to be made.

It is possible to tie certain products together such as Links SQL and VBulletin but even that has to be a seperate plugin just for that function.