Pre validation in Redwood Self Service Procurement page

We have a business case where before submitting a purchase requisition for approval, we need to perform some validations on data, also accessing data in PaaS database. In classic Self Service Procurement, this can be accomplished using Page Composer, adding for example a custom button that opens a custom page where custom reports can be invoked and passing bind variables (for example requisition_header_id).

With Redwood SSP, Page composer is no more available, and Visual Builder should be used instead. Also tried to investigate on preSubmitValidationEvent for "Cart" page, but this seems not working.

Can someone confirm if the above requirement (passing requisition_header_id as variable and launching validation queries before submitting the requisition) can be satisfied in Redwood Self Service Procurement? If not today, there is a planned date where this could be done?