Your timing is good. SailPoint just announced “Forms for Access Request” on July 24. It’s already available in sandboxes (week of Jul 22) and hits production the week of Jul 30.
The feature lets you define custom forms and attach them directly to Roles, Access Profiles, and Entitlements. When a requester selects an item that has an attached form, they get prompted to fill in the additional fields before submitting. So this is exactly the user-input capability that IIQ had and ISC was missing.