> C) patching perltidy to run in a server mode might be a solution.

FWIW:

Actually no patch needed, this code from Perl::Tidy is very fast after initialization (which can take 1-2 secs)

use Perl::Tidy;
 
# ...
# run in a loop reading source and outputting dest
   my $error = Perl::Tidy::perltidy(
                                    argv        => $argv,
                                    source      => \$source_string,
                                    destination => \$dest_string,
                                    stderr      => \$stderr_string,
                                    errorfile   => \$errorfile_string,
+ 
                                   );
[download]

Indenting some lines on laptop took under 0.05 sec and own formatters for "special" html are easily implemented.

(trying to implement a so called "asynchronous process" interface for emacs now)