Might I propose an alternate approach?  We keep the "--length m:n"  
option as is and add a tcp-flags-like list of which objects make up the
final size to compare against:

--length-of IP PROTO PAYLOAD
        or
--length-of ALL

would match the entire packet, and be the default if not specified
so the length module wouldn't change its actions.  This would be the
equivalent of your --length-raw, I think.

--length-of PAYLOAD

would give me the payload size I need. (like your 
--length-payload).

--length-of IP

would allow matching just the IP header, giving an alternate test
for IP options with "--length 21:".  This matches your --length-ipv4, if I
understand you.  I tend to prefer "IP" instead of "IPV4", but don't care
too much either way.

--length-of PROTO

would allow testing for the length of just the protocol header.  
with -p tcp, this would give an alternate test for tcp options too.

--length-of HEADERS

HEADERS would be a macro for IP+PROTO (as ALL is a macro for the
entire packet).  I think we could skip the NONE option.  ;-)

--length-of SOME_MACRO_NAME

would match the PROTO + PAYLOAD.  Any suggestions for a good macro 
name?

	I'm not claiming that all the above combinations are useful (NONE?  
"IP PAYLOAD"?), but this gives a little flexibility to those that need it 
and with carefully chosen macros, not a lot of extra work or typing.

	I'd recommend against trying to break it up into IP IP-OPTIONS 
PROTO PROTO-OPTIONS and PAYLOAD; anyone wanting to test for one of the 
options fields can add 20 to the desired number.
	Since one can express all combinations with postive logic, I don't 
see a need for "!" negation in this parameter.