Oh, wow...companion core in a cheap board would be popular if someone figures out how to leverage it. The OrangePI Allwinner boards are amazingly inexpensive...$10 shipped, including WiFi (https://www.aliexpress.com/store/product/New-Orange-Pi-Zero-...)

Related, the lowRisc RISC-V project has a concept of minion cores: http://www.lowrisc.org/docs/memo-2014-001-tagged-memory-and-...