Re: shift bbpress to sessions
I think the advice you’ve been given is wrong. Public computers are all setup differently, but very few will have cookies disabled.
If you are worried about peoples security, you can disable the “remember me” checkbox on the login form by just removing it from the theme.
This is in bb-templates/kakumei/login-form.php
In any case, moving from cookies to sessions would be difficult as most of the non-login cookie usage is not setup to be pluggable.