I too would appreciate further insight in this specific aspect of this vulnerability. Perhaps with the amount of flexibility apparently available it wouldn't take much work to gain root access.
There are many parallels here to the libstagefright media codec vulnerabilites that were big news in the Android world back in 2015 - the primary problem seems to be remote code execution, not privilege escalation.
It gives you the ability to run arbitrary code with the same privileges as the media player. Going beyond that would require exploiting some other vulnerability to gain root access.
That probably wouldn't be too hard. Local privilege escalation seems to be a lot easier to accomplish. It's harder to secure a system from code running on it than from data coming in from the outside. It's sort of a bigger version of the article's suggestion to "watch out for scripting in unexpected places!"
You also don't necessarily need privilege escalation to do a lot of damage. If the media player isn't sandboxed in some way, then it'll have full privileges to access all your user's files. Traditional UNIX permissions means that you need special access in order to write to the kernel, but not to read your e-mails or that spreadsheet you have with your bank account details.
There are many parallels here to the libstagefright media codec vulnerabilites that were big news in the Android world back in 2015 - the primary problem seems to be remote code execution, not privilege escalation.