I think it’s likely that we won’t change the ordering because other things depend on it (i.e. trying to lay down files owned by a user; the user needs to be created first so we know the UID) but you can always ask the maintainers over at Issues · coreos/ignition · GitHub
For you for now you’d either need to create the users later in the boot process using a systemd unit, or have Ignition create the files in each user’s home dir that you had Ignition create.