Many years ago, a sound engineer friend of mine and myself looked into using Raspberry Pis to build a digital audio workstation. That went nowhere (the Raspberry shield we got to use for the project got discontinued, etc) but the idea still lingers. Commercial DAWs are paired with proprietary hardware to off-load filters to it in real time that is very pricey. It might be possible to use a GPU to off-load some of the filters but of course the issue with any real-time processing of audio is latency.