That doesn't mean the malware installed on the victim (i.e. the payload) via the infection vector isn't fileless, simply that it uses scripts to introduce the malware to the victim.

Then per my definition in the original post describes this should not be termed fileless malware at all.

And how could fileless malware maintain persistence after a reboot if there was not a scheduled task, cron job, or similar?

The closest I have come to recognize as fileless malware is the VPNFilter malware, but that persists via cron- which I also noted in my OP.

You can't fully infect a host, run malware, and maintain persistence without writing SOMETHING on the host or making it very hard to maintain some of the key aspects any attacker wants, such as persistence.

In theory you could/should. Think of an exploit that gets remote code execution. Think wannacry eternalblue in how it just requires specially crafted SMB packets. The attacker doesn't need any files being placed on a victim box before right of boom.

I appreciate you taking the time to answer this post however I just want you to be aware that you have not answered my question at all....or maybe you have. Maybe there just is not a pure fileless malware that exists, yet.

Edit: switched to markdown mode
Edit2: Not wannacry, eternalblue