Flex-objects List view item template

Is there a way to customize flex objects list view using item twig templates?
Suppose we have a “contacts.yaml” blueprint with the following list view part:

# List view
list:
  title: name
  fields:
    published:
      field:
        type: toggle
        label: Publ
      width: 8
    last_name:
      link: edit
    first_name:
      link: edit
    friends:
      field:
        label: Number of Friends
        template: '{{ friends|length }}'

I would like to see a number of “friends” in the last data-column. The field “friends” has a list type. But the above code does not work for me. The “template” setting is ignored. Is it impossible? Help me, please.