Cannot filter lists using child doctype

[nabilshuja]

Frappe allows getting a list of Doctype with filters applied on Child Doctype.
For example, address here could be filtered using Dynamic Link

Ideally I believe, DBFilterInput could allow input of doctype option that is non-mandatory. Which would be manipulated purposefully for filter usage..

input DBFilterInput {
  doctype: String
  fieldname: String!
  operator: DBFilterOperator
  value: String!
}