I'd expect it to be less than 6000 based on what I see in the game. Couldn't see there being many more than 1500-2000 unique players on Citadel regularly, and it's the biggest server, (unless the Russian server is massive). So I'd say 3-4000 for the whole game. (Could be wrong obviously)
Matt's earliest posts in that thread show the number of tickets going up by 800 - 1300 a week. That would be equivalent to somewhere between 20 & 25% of the playerbase making a ticket a week if my read on the overall numbers is about right. Of course, it's very unlikely that everyone playing makes a ticket once every 4-5 weeks on the nose. It's actually more likely that 1% of the playerbase makes 90% of the tickets, and I bet most of them amount to whining about being scammed, banned, being killed by better players etc. etc.
tl;dr, a small number of people are probably flooding Support with useless shit.
And then about 10-20% of the remaining playerbase put in the rest of the tickets that are legit things to contact support about, that get delayed because of having to sift through shit.
G1's support sucked and now LO's is struggling under the volume they have. What's the common factor? The people sending in the tickets.