BackBeat was made for bass players in mind because of the lack of tactile feedback monitoring in the subwoofer frequency range. This range also crosses over with lower (E and A) strings on an electric guitar, and with 7-string guitars. However, BackBeat will not shake across the full guitar range. We are working on a BackBeat version for guitarists who play only with IEMs.
BackBeat will work with any electrical signal sent to its input. If your double bass has a pickup that generates an electrical signal, BackBeat will shake at frequencies below around 150-200Hz. If you have an electric drum set or mic-ed drums, you can send a mixed signal to BackBeat and you will feel your kickdrum, toms etc.
Eventually yes, it is a possibility. For this first revision of BackBeat, we're keeping it as accessible as possible with the best features available. As BackBeat grows and demand increases, we will start integrating other technologies.