Adding the feature to enable filtering button on the first row of the generated spreadsheet output would keep the design output consistent with the same functionality that the Kendo grid is providing today with the generated spreadsheet export using the parameter "filterable: true". Please check the Support ID:1362164 for more details.

Excel Autofilter in combination to SpreadStreamProcessing would be great!

It could look like this:

namespace Telerik.Documents.SpreadsheetStreaming
{
    // Summary:
    //     Represent the base class for cell formats.
    public abstract class SpreadCellFormatBase
    {
        protected SpreadCellFormatBase();

        public bool EnableAutoFilter { get; set; }
    }
}