> Can you elaborate

What to eleborate here? You want a new feature for emacsclient so you go
and patch C source. Tomorrow you'l want a new commandline option.
So why no one here think about general solutions?

Emacslisp solution is always better than C. (Hooks, hooks must be
everywhere in emacs)

How it could be implemented:
(I'd say that we can use the same command-line-functions and
command-switch-alist but it could break backward compatibility, so it'll
better to use a new variables I think -- emacs-client-argumet-string or
something.)

1. emacsclient searches for 'connection related' arguments because they are
needed to know how to connect to the daemon.
2. emacsclient sends the full arguments string to the server.
3. server calls user(and predefined) hooks which must examine and do
manipulations on that string.