We are using the Kendo UI spreadsheet in a real-world website. We have a design team who are providing a visual design which fits in with our company's corporate standards.

HTML5 aims at separating styling from the layout design, which enables different teams to build the syle, with very little development experience, but more artistic experience.

For some reason, the Spreadsheet control can only be styled via the API (javascript code)! This means our design team needs to write their style in javascript, which is completely unrealistic.

It should be a fairly simple change to allow a range object to have a CSS class associated, and let HTML work like it should.

In the scpreadsheet you can use controls like  dropdowns & datepicker , but should be helpful if user could to customize the design and behavior. 

For example, the dropdown and any other control needs be opened since an icon at right that is displayed over the next column, As user i would like to choose how i want to be displayed the control: Open clicking on it, set expand direction, styles, etc.

Support scenarios where users can use the spreadsheet component to design templates with disabled cells.

I appreciate that this can be customized (as almost anything) but note this is the only cell property that is not configurable via the toolbar.

Add menu item that allows end users to style background and text color based on rules (if cell value > 0 then green)

can add float object container ? eg:charts

Need a default cell format, in addition to rowHeight and columnWidth including:
- font size,
- font-family,
- font weight
- (see other toolbar options)

Default cell format would set the default values for all cells and toolbar options.

Enable Cut/Copy cell values and can Paste it in mutiple selected values

On excel, you can filter merged rows. On the kendo spreadsheet widget, filtering on merged rows is not possible. It would be a very useful feature for us. 

Also worth noting is that if you convert an excel file to JSON using Telerik RadSpreadProcessing, and load the kendo widget with the JSON, the widget displays a filter icon but clicking it loads a non-functioning filter. Wouldn't it make more sense to load with a message along the lines of 'You loaded a spreadsheet with filters applied to merged rows, which is not supported in this widget'. Otherwise it's quite confusing to our users.

E.g. italian culture uses ";" as parameter separator in formulae.
Our client will adopt spreadsheet component on a global basis and users need to be able to e.g. copy/paste from excel to spreadsheet component using their culture

Currently if I set column border width large, it has multiple problems:

1. it will overlay on columns next to it;
2. when copy the cell with thick border and paste somewhere else, the thick border get copied as well;
3. when select cell with thick border, the border will block part of editor;

Right now, a List based validation is strict on case, it'd be nice to have a toggle for when it is appropriate.

Use case:
My app doesn't know how many rows of data the excel spreadsheet will be prior to upload.  I've defaulted to my maximum amount of 10,000 which will be normal for some, but overkill for others.  The ability to change the number of rows/columns to accommodate the size of the sheet after loading, would be a nice addition.  

As a workaround, I'm destroying and reloading the widget instance after the initial load.

This will help doing data entry in column for scenarios like entering tax details for different years in columns and also user can keep on entering new year info in rew-row right most column.

Be able to edit an spreadsheet by several users at the same time, reflecting the changes from one user to the others and viceversa.

In Kendo UI spreadsheet when wrap cell text it currently split text in middle of word. Change so that splits on white space

Ability for spreadsheet row height to be auto set from the row contents. This is to support wrapped text.

Ability to hide a sheet in kendo spreadsheet

Ability to hover over a cell and see a tooltip

1. Save Excel workbook to folder on server (the Excel file can be re-purposed in many ways)
2. Better ways to send sheet data back to controller ... more JSON serialization options, csv, etc.

We'd need support for checkboxes columns in the new Spreadsheet control.