Are we truly to be limited by this convention regarding bar rests in longer meters (such as 12/4 in the example below) where the rest is an upward rectangle. There are times (cadenzas for example, where a long meter and a hidden time signature), where a garden variety bar rest would be preferable, especially since we get those by default in unmeasured metre. I couldn’t find a setting, or a reference to this on the forum.
You’re quite right that at present there is no option for this. We will look into adding an option to limit bar rests to a whole note (semibreve) in duration at some point in the future.