I would like to have a preview and/or debugging function as well.
You can create a feature request and hope for an implementation.
"Workaround" for me in some cases:
As long as your desired function is working in request offerings, you can create some dummy parameters and add this function as a reference:
Similar to Florian but I use an update quick action in my staging environment on the Incident description field, the main reason for this is that not all functions are supported in the Service Request form designer.