How do I change the color scheme? (I know, hack the code. But the colors really should be in a configuration file.)
Ditto, the font. (Again, I can mod the code, but putting meta-data like colours and fonts into a config-file is really better in the long run. More maintainable -- changing your code should not effect my custom settings.)
Maybe allow the User to specify which key words get which colour. (I know I am building an enormous config file. But you can group things and set default colors that the user can over ride. For example -- "subroutine => 'yellow'; "subroutine this_sub => 'orange'" in the config-file will highlight all subroutine names in yellow except 'this_sub'.)
Would it be useful to highlight packages when they are used in identifiers -- $My::Package::new() gets "My::Package::" in 'medium-yellow' and "new()" gets rendered in 'bright-yellow". It will be gaudy, but my production code is littered with these constructs. It often gets hard to find the subroutine for all of the package qualification. (my $next_curve_ref = $estimate -> Statistics::Kerman::NonLinear::Approximation::Regression::CubicSpline::new() for example.)
It would be very useful to have the current line number displayed. (And updated as the cursor moves.)
Have you thought about highlighting opening and closing braces? (Brackets and Parenthesis are less likely to find themselves separated by a couple dozen lines. (An aside; I have just ran across a production module last week where the line number of the opening brace is 110 and the closing brace is on line 1044; one hulluva 'if' statement. Major refactoring project, starting tomorrow...)