While that's nice and all, this won't most likely get implemented to speed servers. Like 90% of speed server population is basically newbies who want to spawnkill everyone all the time. People would just stop coming to the speed server and go to some other, which doesn't have this (by people i mean speedstars obviously). Mainly because getting kicked is an inconvenience, which can be avoided by switching other server.
What i think would make more sense, would be just ending the round as soon as you detect signs of spawnkilling. I am not sure if this could be implemented using the same method you used (or if it could be implemented at all), but this way you stop spawnkilling from happening and remove the easy way how to get 'good' score.
I think that what i suggested is the only 'non-violent' way to work around spawnkilling. By violent i mean kicking someone, which people would never appreciate. Spawnkilling isn't in sense wrong, yea its annoying, but its how the game works, you can't just kick someone for using the game mechanics to their advantage. Another possible solution might be to just kill the person who gets detected as 'spawnkiller'.
PS:One major flaw i see right now, is how do you deal with multiple spawnkillers. The way speed server works is that if one guy spawnkills, others will follow. They can get easily to the spawn, because one guy is spawnkilling some people. Server would just fill chat with warning messages, making them casual and not worthy reading. Especially for newbies on speed, who don't even know how to use chat for anything else except for "OMG LAG", "TEAMS" or "prozajik hacker".
I had troubles reading messages for just one guy you posted above (mostly message STOP SPAWNKILLING), doubt anyone will be able to follow messages like that for 4 guys.
Fix:Write only 1-2 messages for everyone.