if i dont missunderstood what @semlohj wish it is already possible:
at backend primary with the help of the clone-field.
for the frontend with help of includes that contains the reusable block.
- create option page, that dont need to be accessible for general / by menu
- create a fieldgroup with all needed fields inside (everything inside repeater but not repeater itself) assign it to that optionpage
- create new fieldgroup with repeater and add a clone field that use all field from above group
- create an other fieldgroup/repeater-field/flexible-field and add a clone field that use all field from above group
with help of that, you can update the original fieldgroup and the changes apply to the clones
i do for example:
fieldgroup teaserbox = text,textarea,image,link
fieldgroup halfcolum = flexible-field with a layout, that include clone-field:teaserbox
fieldgroup fullcolumn = flexible-field with a layout, that include a repeater with clone-field:teaserbox inside
fieldgroup content = flexible-field with 2 layout, one inlude clone-field:fullcolum || the other include prefixed clone-field: halfcolumn, prefixed clone-field: halfcolumn
now i can add another field to teaserbox and fullcolumn, left_halfcolumn, right_halfcolumn where updated
hope that help. else may @acf-support can reproduce what i say and give a more detailed answer
