Commandline headless options are great and versatile.
What's missing is update and print form letter.
That would be useful for usage but also for LO QA and bug triage.
Update (yes, no) if file contains links to external data is analogous to GUI question. No should be default.
GUI also also asks whether to print form letter / serial print / mail merge.
That's missing now, current print command --pt will just print document as seen.
Form letter offers options to print all records or selection but all is fine.
Form letter can print to printer or to file.
Printer is more simple, no need for additional arguments and just option --form would be nice.
Print to file has options single or individual files, location.