So here is list of classes and files, that may be subject to change, including the name of the method, where the changes may be made:
plugins/fabrik_element/databasejoin/databasejoin.php PlgFabrik_ElementDatabasejoin extends PlgFabrik_ElementList
::getAsField_html(&$aFields, &$aAsFields, $opts = array())
plugins/fabrik_element/user/user.php PlgFabrik_ElementUser extends PlgFabrik_DatbaseJoin
::isHidden()
::getAsField_html(&$aFields, &$aAsFields, $opts = array())
::getFilterQuery($key, $condition, $value, $originalValue, $type = 'normal', $evalFilter = '0')
components/com_fabrik/models/elementlist.php PlgFabrik_ElementList extends PlgFabrik_Element
::renderListData($data, stdClass&$thisRow, $opts=array()) there is an explicit reference to PlgFabrik_ElementDatabasejoin
components/com_fabrik/models/element.php PlgFabrik_Element
::buildQueryElementConcat($jKey, $addAs = true)
::buildQueryElementConcatRaw()
::getFullName($useStep = true, $incRepeatGroup = true)
::getJoinIdKey($step = true)
::getJoinParamsKey($step = true)
components/com_fabrik/models/list.php (FabrikFEModelList
::addSelectBoxAndLinks(&$data, $opts = array())
::getTableLinks() a reference to ?#_menu? is made (may be must preceded by database name)
components/com_fabrik/models/join.php FabrikFEModelJoin because this is a central place for Joins
components/com_fabrik/models/connection.php FabrikFEModelConnection ?probably no changes needed
components/com_fabrik/helpers/parent.php FabrikWorker ...probably no changes needed
plugins/fabrik_form/comment/comment.php FabrikTableComment
::getComments($formId, $rowId)
Should we discuss the changes here? I think it would be better to create an issue in the GitHub system. Because I is a bigger change, the details should be discussed to get a rounded up result that fits the needs of most of the users.