We need to display a custom content in the grouping cells (the empty leftmost indentation cells in data rows). Currently it is impossible since the cells are rendered "statically" (kendo.grid.js, line 337):

function groupCells(count) {
    return new Array(count + 1).join('<td class="k-group-cell">&nbsp;</td>');
}

Currently I insert my cell content AFTER the rows are rendered using $('.k-group-cell', row).html(...). But, you know, it is far not the best approach.

Please implement a grid option, say, groupCellTemplate:string|object – it won't be too hard. And let me know if you would like me to contribute.