I think that showing the number of followers in the issue list would be very convenient feature as it will provide an easy way to prioritize issues. (Fixing the bug experienced by the most users usually have biggest net benefit rather than fixing the one encountered only by a few users.)
We've just rolled out improvements to the issues list screen, and we're as pressed for room as we ever were (in part thanks to the inclusion of the much-requested "priority" field). While the argument in favour of adding a "number of followers" column is sound, there are six existing columns which we deem more important.
While not ideal, it's now at least possible to go through the list of issues and adjust each issue's priority in accordance with its popularity.