ETA for Linux Nodes?

Isn’t there already an updater for the docker version, i.e. watchtower? Is there a better way to update on the way?

If you use a docker version, then only watchtower (any platform and OS).
If you use a binary version (Windows GUI, [Tech Preview] Linux Installer Part 2 or [Tech Preview] Linux Storage Node & Updater), it comes with storagenode-updater as well.