I think these types of choices boil down to personal preference, usually gained from other sites we frequent. If you wanted to be
totally diplomatic about it, you could introduce a poll for a period of time that will span through our next meeting, where it could be announced and thereby get the (hopefully) most amount of participants. Or, it might just be simpler to make an "Executive Decision" on what you feel is right. You, after all are Sheriff around here...

...it is in your best interest to incorporate features you feel are logical and therefore "enjoy" maintaining...it's less of a chore that way. We'll adapt to what is given to us.
Although I see Fred's logic with the second-level forum within the appropriate genre...I'm not sure we have the volume of users to require segregating WIP's from discussion and display threads...that's just my opinion...but in the spirit of "
keeping it simple", I like the idea of prefixing WIP threads with "WIP-" (so much so, that I went back and re-titled my appropriate threads...you can slap my hand if I jumped the gun Ray...

)...this will also reduce the need for the Admin to police the forums so much...you won't need to be relocating WIP threads from the "X" Forum into the appropriate WIP Forum or Section.
That would be my (rather long-winded) opinion...
Cheers