Upon learning that Raspberry Pi 3 and above has PXE boot capabilities, I pulled out my dust gathering, poor Raspberry Pi 3B... My motive is NOT to re-image that MicroSD card every time I want to tinker stuff, simply plug-in, power up, and viola, at least ideally.
Following the guidelines from various sources:
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/net_tutorial.md https://help.ubuntu.com/community/DisklessUbuntuHowto