Good pointg re BT.... radio, I guess it would have to be.... course, that's already done for wireless connections between guitar and amp, seems no reason that couldn't be adapted to incorporate an earpiece?
By twinning them, are you essentially looking at making it 'two channel'? I've been very impressed by what I've seen from Joyo et al. Sure, a lot of it is copied, but so is most guitar stuff by this point.