I disagree that a new forum on sharpening would require additional sub-forums. I've heard similar comments on other discussion boards when a new category is requested. In my case, the need for nested categories never occured and the discussions flowed nicely.
If enough members are asking for this, why not give it a try and see how it goes? A dedicated forum for all sharpening discussions could be seeded with selected discussions from other areas to get things started. If it doesn't work out, then dump the threads in to the Neanderthal Haven forum.