Have you look at Google's new Rapid Bucket offering? Google Cloud Storage is arguably as good as S3, and is protocol compatible; Rapid Buckets are a type of bucket which supports appendable objects and low latency I/O. The downside is they can only be zonal, and they're a bit more expensive.
PicoMQ works with any S3-compatible object store. But I wasn't aware of GCS Rapid Bucket, it sounds a lot like AWS S3 Express, which is also zonal. And it does help with durability ACK latency quite a bit, keeping it closer to ~50ms.
I'll be setting up a GCP deployment example similar to AWS soon. I'll be sure to try Rapid Bucket as well, thanks for sharing!