In addition to the fast document generation, the SpreadStreamProcessing can be adapted to import documents significantly faster than SpreadProcessing.
At the moment only the XLSX and CSV formats are supported. It would be a good idea to add the TXT format as well.
Expose an option to overwrite a sheet if it already exists in the workbook.
Provide a way to measure text on different platforms so the user can pass the cell value and SpreadCellFormat and get the size of the text in pixels. This way we will be able to implement auto-fit to width functionality (AutoFitWidth), at least for the .NET Framework implementation. It will be able to measure the width of all cells in a column and set the value as column width in pixels.
Sheets can have Visible, Hidden and Very Hidden visibility. Add support for setting this property.
The UTF8 with BOM encoding should be used to properly preserve the different characters. Available in R3 2017 Official Release.
Add API for appending data to existing worksheets. This way data could be filled in template documents.
The customers should have the ability to change the symbol used as a delimiter and the symbol used as a quote for a CSV document.
Add support for creating Tables and applying tables styles (predefined ones, similar to MS Excel, or custom).
Add support for Data Validation.