Sorry if this has been asked/discussed before:
I just tried making a rounded version of my font using a custom parameter for the instance. Works as expected when I export an OTF. However, when I select the instance for the preview then it does not show the rounded corners.
I wouldn’t go as far as to call it a bug but hey, wouldn’t it be super cool to have an instant rounded preview as you edit the source shape?
I guess with custom parameter preview working, there could be other interesting things one could do with it.