I'm not all that interested in slipjoints, but I do really enjoy BladeForums due to my enjoyment of knives and the great discussion & info provided by forumites (birds of a feather and all that). As I read more and learn more I gain interest in new blades, and have purchased a few (MT Tachyon on the way this week, plenty of cuts by next week). Spark has given the criteria for a new forum in this statement:
1. There must be a need for it
2. There must be sustainable traffic for it - not just the initial "pop"
3. There must be qualified moderators.
You folks seem to have #3 squared away (Gus, Nifrand and Buzzbait), provided they meet Spark's approval. Do they?
#1 should be able to be proven out objectively without too much trouble, if you folks are *really* interested. What % of the knife market are slipjoints? How many companies and custom builders are there and how does that compare? What is the ave. cost of a slipjoint (available to more consumers?) and how does that compare? What type of knife is most often carried and where do slipjoints fall into the ranking? Slipjoints are part of the maturation process of the "blade" in general....what is the history of the slipjoint? How many forumites on BladeForums own a slipjoint?
#2 also should be fairly easy to determine. Someone mentioned 300+ posts in the last few months - how does that compare to other forums in the same time frame? Establish a baseline, give comparisons and then sell the idea.
If you've provided objective facts, then all that remains are the subjective aspects of the decision. Of course then there's always, "if you build it they will come"

. Good luck folks, I'm headed back to my other fav forums and will hopefully add slipjoints to the list in the near future. All I have now are the ones my Dad & Grand Dad handed down to me (hint hint - proves longevity of this type of knife!).