I updated the plunker with the solution (last grid shown).
http://plnkr.co/edit/taPmlwLxZrF10jwwb1FX?p=preview
The idea is that you should 'talk to ng-grid' exactly like the other editablCellTemplates do. These 'rules' aren't well defined in the documentation, but they could be deduced by looking at ng-grid's source code for the ng-input directive.
Basically, your own component should respond to the ngGridEventStartCellEdit event by focusing your editor element, and the most important thing is: your component MUST emit the ngGridEventEndCellEdit event only when the cell loses focus (or when you want the editor to disappear, like maybe when pressing enter or something).
So for this specific case I created my own directive that adds the necessary behaviour to a ui-select2 element, but I imagine you could understand what you'd have to do for your own specific case.
So, as an example, here is my ui-select2 specific directive:
app.directive(
'uiSelect2EditableCellTemplate',
[
function() {
return {
restrict: "A",
link: function ( scope, elm, attrs ) {
//make sure the id is set, so we can focus the ui-select2 by ID later on (because its ID will be generated from our id if we have one)
elm.attr( "id", "input-" + scope.col.index + "-" + scope.row.rowIndex );
elm.on( 'click', function( evt ) {
evt.stopPropagation();
} );
elm.on( 'mousedown', function( evt ) {
evt.stopPropagation();
} );
//select2 has its own blur event !
elm.on( 'select2-blur',
function ( event ) {
scope.$emit( 'ngGridEventEndCellEdit' );
}
);
scope.$on( 'ngGridEventStartCellEdit', function () {
//Event is fired BEFORE the new elements are part of the DOM, so try to set the focus after a timeout
setTimeout( function () {
$( "#s2id_" + elm[0].id ).select2( 'open' );
}, 10 );
} );
}
};
}
]
);
and my own editableCellTemplate would have to look something like this:
$scope.cellTemplateDropdownUiSelect3 =
'<select ui-select2-editable-cell-template ui-select2 ng-model="COL_FIELD" style="width: 90%" >' +
'<option ng-repeat="(fkid, fkrow) in fkvalues_country" value="{{fkid}}" ng-selected="COL_FIELD == fkid" >{{fkrow}} ({{fkid}})</option>' +
'</select>' ;
A little bit of 'official' information can be found here: https://github.com/angular-ui/ng-grid/blob/master/CHANGELOG.md#editing-cells