Thank you for your interest in Aspose.Slides.
I have observed your comments and like to share with you that I have logged a feature request with ID SLIDESJAVA-35146 into our issue management system, for further investigation and resolution. For now, you may use the feature of generating thumbnail of a shape and then adding that to some slide for generating the PDF. This is the possible workaround, until the feature is supported. This thread has been linked with the issue so that you may be notified automatically as soon as the issue will be fixed.
Please share if I may help you further in this regard,