It is easy to offer this option to the user per configuration.
The following addition to the setup.tex.in
as well as subsequent patching should do:
\usepackage{bookmark}
\bookmarksetup{
open,
openlevel=2,%3 if toclevel=3 we need set it here
numbered,
}
Implemented with release 2023.1.10 - as is (without the commentary and without customization).