{#pane_current_command} seems to contain only the name of the running executable, without the arguments passed to it. Can the arguments be retrieved in a simple way?
I know of ps -o state= -o args= -t PANE_TTY, but I haven't found a way to use the result from within a tmux command, such as set -g pane-border-format "COMMAND_AND_ARGS".
set -g pane-border-format '#(ps -o state= -o args= -t #{pane_tty})', but you will not like the way it gets (or rather sometimes doesn't get) updated.