Just a thought - if you build up a list of participating toons' names (from chat/tell lines) in a first pass of the file, you could then check for chat lines starting with any of those names. Those that do will be emotes and/or a subset of the system messages.
Assuming the system messages are pretty boilerplate ("X has defeated Y") you could identify a good number of those too.
All more work than you'd need if the "[System]"-type tags you've suggested were in, of course, and quite possibly something you've already thought of! 
I considered that, and something along those lines is probably what I'm going to have to do until the devs do the nice thing. 
Still, it makes for messy code having to do stuff like that, and I'd really rather avoid it if I could...
@FloatingFatMan
Do not go gentle into that good night.
Rage, rage against the dying of the light.
Time stamps in game would be nice too.
OK, this is more of a QoL request than a suggestion, but this is the only place I can post it really. Hopefully GR can do me the favour of sending it on to the devs!
Anyway, I've recently been working, off and on, with a Chatlog parsing program, primarily for the use of myself and fellow RPers, but it would be useful for anyone really.
However, I've got a little snag with how some things are logged that's making some things impossible; mainly, it's how system messages and emote text are logged.
For example. System and combat messages look like this:
[ QUOTE ]
06-30-2008 00:01:53 Entering Portal Court.
06-30-2008 00:01:54 Welcome to City of Heroes, Tiger White!
06-30-2008 00:01:55 Using global chat handle @FloatingFatMan
06-30-2008 00:01:55 Joined channel 'GGOOC'
06-30-2008 00:01:55 You have 1 email
06-30-2008 00:01:56 You have 4 unclaimed respecs available.
06-30-2008 00:01:56 You have 12 unclaimed free tailor sessions available.
06-30-2008 00:20:29 You are flying!
06-30-2008 00:20:35 Shutting off Fly.
06-30-2008 00:20:35 You are no longer flying.
06-30-2008 00:22:27 Arthuria has defeated Void Seeker
[/ QUOTE ]
Whereas emotes look like this.
[ QUOTE ]
06-30-2008 22:34:38 Tiger White rolls her eyes
06-30-2008 22:34:50 Canada Red grins
[/ QUOTE ]
Code wise, it's impossible to differentiate between system, combat and emotes (and some others to). What I'm asking for is for tags to be added to all lines of text, to indicate what they are, IE:
[ QUOTE ]
06-30-2008 00:01:55 [System] You have 1 email
06-30-2008 00:20:35 [Combat] Shutting off Fly.
06-30-2008 00:20:35 [System] You are no longer flying.
06-30-2008 00:22:27 [Combat] Arthuria has defeated Void Seeker
06-30-2008 22:34:38 [Emote] Tiger White rolls her eyes
[/ QUOTE ]
It's a very small change, and I know it would only really benefit a small number of people; but it would be of MASSIVE use to those who DO use it. Almost every other type of line in the logs is tagged with what the text is, all I'm really asking is for ALL lines to be tagged with identifiers. Pretty please?
Oh, and also... There's REALLY no need to include speech bubble colour coding information in the logs.. Makes them a bugger to read, but I can filter those out myself if need be; the untagged lines, I can't.
Anyway... I'm gonna finish my chatlog parser, but without a way to differentiate all lines, filtered logs will NEVER look as tidy as they could be without a load of manual editing.
@FloatingFatMan
Do not go gentle into that good night.
Rage, rage against the dying of the light.