@piet shs is secret-handshake. I think most of the work with changing to async crypto is rewriting the javascript, especially the parts of the application that assume a function is gonna be sync.

If you really wanna get your low level hands dirty
I think the most enabling thing here would be a proper fs interface.
It would need open, read, write, stat, readdir, mkdir, ftruncate, fsync, fdatasync, close ... just the low level functions in the fs module, i.e. the ones that are about file descriptors instead of paths.

This will enable flume & blobs (and the various other things that use fs)