I see groups requesting healers/dps/tanks. Bard and chanters are rare and in need, but half (or more) of the folks playing other classes have no idea they need them! I was level 45 before I grouped with an Enchanter on Faydark.
On the upside, if you start a bard/chanter you can usually get Adept/Masters for them (try it with a Templar)...cause they are just rotting on PC vendors.
A handy thing to do, since servers vary, is to do a /who all Illusionist 20 30 (30 40, 40 50...etc) to check and see how many are active on your server during your play time.
You can also go to EQ2Player.com and look at Sony's totals for a given server, although you can't tell how many are actually playing by those numbers.
As far as your other post, I don't think Coercer/Illusionist would make much difference. I have a 31 Illsusionist and havn't played a Coercer but both at high levels seem to do well at crowd control when it exists.
In EQ2, most groups do crowd control by keeping the tank alive, him taunting, and burning down his targets. Tanks typically pull in EQ2 as well. You could very easily get a group as a chanter and just do group buffs and dps. Many groups either have no concept of crowd control or just don't want (and sometimes don't need) it.
AE mezz is sometimes used in high level raids, but it doesn't stick as reliably as you'd like on some targets. Lull/harmony exists but my Templar is the only one I have ever seen use it. Mezz and Fear is used in knowledgable groups, but not as much as you'd expect, having played EQI. 7 out of 10 groups would be looking for a mana battery and dps.