InfluxDB creator here. I've actually been working on this one myself and am excited to answer any questions. The project is InfluxDB IOx (short for iron oxide, pronounced eye-ox). Among other things, it's an in-memory columnar database with object storage as the persistence layer.

The architecture you've proposed here has many overlaps with q/KDB (or Jd, Shakti), which does not (AFAIK) have a decent open source alternative. Looking forward to see what you build!