Allowing custom editors to be inline would be very helpful. In particular, inline editors using other Kendo controls (e.g. masked textbox, numeric textbox) should be possible.

Custom editors are great!  But often when you have a custom editor, you want to restrict data entry to only use that editor, and not free-form typing in the cell.  You can prevent free-form typing in the cell by disabling the cell, but then the custom editor button is no longer available.

Suggestion is to still show custom editor button even if cell is disabled, perhaps with an additional setting; so that you could optionally not show the custom editor if the cell is disabled, since often a disabled cell should prevent any kind of modification.

Currently the spreadsheet dynamically creates the FilterMenu for a range, that is, it's not created until someone clicks the filter dropdown, and it's destroyed if they switched tabs.

There is no event that is fired when these things happen, which makes it hard to attach to, and customize, the FilterMenu without setting up some crazy listening code (setTimeout, etc.). 

It would be great if either (or both:
- You could specify a template for the filter menu.
- You could listen for a "FilterMenu Initialized" event and capture the menu there and customize it.

Add ability to add group multiple columns and add a group header for those columns.

Can we have a facility to copy a cell and paste it to a selection. (i.e paste to multiple cells)

By default the items in filter are in random order. Can we sort the items in ascending order by default.

The current context menu lets you hide a row or column, but then you cannot show it again, so the user can lose data. At present there is no context menu option to unhide it and there is no element indicating the column/row was there in the first place. This should behave like in Excel.

We have clients with large spreadsheets that print out across multiple pages, which can mean losing track of which column refers to what on new pages after a page break, so they want to be able to assign a row of column headers to be printed on new pages above each column to keep track

Currently if you access cells range programmatically, you can set background color, text color etc.
It would be good to have the way to set classes or to get the DOM of the range.
Another option would be to get DOM or set a class to individual cells (e.g. via range.forEachCell).

Presently in Spreadsheet tooltip is not working for filter applied range 
so tooltip should display for each cell in which the range of filter is applied

I know that Kendo Spreadsheet works like most popular Spreadsheets (Excel and Google Spreadsheet) where, if you copy or drag and paste values from cells, you will copy also the styles, validations, etc from that cell to the new one (unless you select "paste values only" in a context menu or ctrl + shift + v). 

It would be awesome if we can set how this works by configuring a property in the Spreadsheet configuration, something like pasteValuesOnly: false/true or even more complex with an object where you can choose if paste values, validations, formulas, styles or whatever. Also you could attach this functionalities to a context menu (as Google Spreadsheet does) and be able to paste everything, values only, format only, formulas or data validation.

Can the Spreadsheet widget be updated to initialize a sheet that is bound to a datasource when the datasource is an empty object?  

Generally, when a sheet is bound to a datasource, it is for the purpose of editing data, creating new rows and updating/deleting existing rows.  If a datasource comes back empty, the sheet isn't initialized.  So there are no column headers, which can be confusing to users when they don't know what data to enter in which columns.  The other thing is that the sheet itself is not fully initialize so that even if we assign column headers programmatically, when users start entering data, the UI becomes unresponsive and generates a javascript error: Uncaught TypeError: Cannot read property 'indexOf' of undefined
    at r.set (kendo.all.js:4586)
    at r.set (kendo.all.js:4760)
    at kendo.all.js:127702

Set an indicator same way that grid already does but now in sheet cells when a record is 'dirty'.

DefaultCellStyle property in spreadsheet has a field “Wrap”, but doesn’t have a field “Format”. For example, if I need to process all cells as text, I must set the field “Format” on a client side:
sheet.range("A1:AX200").wrap(true).format("@");
It works.
But the initialization of the range ("A1:AX200") takes time… It is not very fast…
It would be better to have the field “Format” in the DefaultCellStyle property in spreadsheet…

I need the way to get a user the opportunity to set the columns headers. Moreover, the columns headers should be saved separately from the main spreadsheet data.

Of course, the possible variant is to have two spreadsheets: the one – for the data, the second (with one row) – for the headers.

But the better way is to get a user the opportunity to set the spreadsheet columns headers.
It would be ideally if a user could change “A”, “B”, “C” for “ID”, “Product”, “Quantity” …
Not to have a first row for headers, but change the spreadsheet columns headers!
Moreover, we have the context menu on the columns headers and it is possible to add one more item “Edit” in it.

I am working on a project where i am using KendoUI components. I have to show a financial sheet. All formulas are working fine like SUM,INDIRECT etc. but IRR not working as expected.

Tested IRR formula outside my project and the same happened.

Additional functionality for:
-- Conditional Formatting -- coloring of cells, for example based upon a value and then be able to import from excel, and export back out.
-- Data Validation (dropdowns).  Also be able to import and export back out.

It would be useful if copy and paste the data have the option of fill the series or copy the value for the date format. 
Furthermore, copy from multiple column value and allow to paste multiple copied value from the spreadsheet will be added advantage. 

Thanks. 

For KendoUI Spreadsheet, it should have the ability to add images or logo into the spreadsheet. This feature is already available in Handsontable component.