Rqlite is an awesome project but it's not intended for use above a couple GB, like etcd. Sorry, dataset size is what I meant by cluster-size which was a confusing way to put it. You're right, I don't care about the number of nodes in the cluster.
That said, very large datasets (> 2GB) will work, if you've got the disks and memory to handle it. The link above explains how to do it.