Addition: 'Translation'/'Internationalization' and 'Usability' are probably another two of these "hot topics". smk-ka just pointed out, that we already have a template for this topic list at http://groups.drupal.org (it's called '[interest] group' there ;) If we provide the right tools for interested users, I'm pretty sure they will contribute more.
Middle-term proposal: Categorization of issues has just been enabled for 'Newbie' and 'GHOP' terms. Why don't we add another vocabulary for global issue categories like 'PostGreSQL', 'Performance', 'JavaScript', etc. ? That way, contributors who like to focus or help out on a certain topic could easily *find* all related issues (and probably subscribe to a feed). If that categorization was also open for contrib modules, overall support for postgres and the like may be increased. Realization of this proposal would include that the category of an issue could be altered in an issue follow-up, and not just at the time of issue creation. Furthermore, we should provide easy access to those categorized issues - the 'contributor links' block jumps into my mind immediately.
Daniel