On a serious note.
If it's entirely separate from BC, that's a different forum and I think it's a bit of an ask to want the guys who run BC to set up and run another forum.
If it's accommodated within BC it runs the risk of changing the character of the place and possibly alienating some members. There's a good vibe on here and I for one wouldn't want to see anything brought in that changed that. If you place an 'Other Instruments' forum on BC that is available to non members to peruse, then you risk the forum attracting people who haven't the passion or dedication, like Ped and the team, to create their own forum for their own particular interest.
From a personal point and a selfish one I admit, I only play bass. I don't, can't and have no particular interest at the moment in learning another instrument. If the forum was to be turned into a quasi multi instrumentalist forum I think I might loose interest. Of course some might say that would be a good thing.
It may seem OTT but I really enjoy BC and wouldn't want to see something brought in that damages its character or vibe.
I am not saying it shouldn't be considered, but that it should be done with all possible outcomes, positive and negative, taken into account.