While I'm here posting my own suggestion, I figure I'll add my thoughts.
Isn't the M16 - Full Auto forum enough? It's not like it's overflowing with traffic. All that would need to be done would be add a caption underneath "M16 - Full Auto" that said "Anything Class III, Suppressors, SBRs/SBSes/AOWs".
I don't think ARFcom has enough traffic in the entire Class III department to merit a single forum for suppressors alone. I don't think creating a million different forum sections doesn't gather new users, an example is the General section. There's a dozen sub-forums that have next to zero traffic in them.
I should add I'm not anti-supressor or anything... we all need to dream (like I dream of not living in Michigan), I just don't think the M16 forum is overflowing with supressor Q & A's.