As per this forum post: http://www.kendoui.com//forums/mvc/grid/bug-grouping-name-does-not-honor-mvc-attributes.aspx, the MVC Helpers for the Grid honor the Display attribute in certain situations, but not others.Namely, when a column with a [Display] attribute is turned into a Group, the DisplayAttribute.Name is no longer honored.

But even that is technically not the correct behavior. The correct behavior is for the group to use DisplayAttribute.GroupName, then DisplayAttribute.Name if the GroupName is not specified.

For KendoUI Mobile, it would be great to have a controle that display an alphabetical index (a-z), much like the Windows Phone 7 jump list. 

This could be bound to the first letter filter property of a list control (grid or else). 

Rather than working on you own MVVM implementation you should provide support for full KnockoutJS as other vendors like Infragistics & ComponentOne have done. Very few of us would want to get tied with your MVVM implementation which would make moving to other controls in future difficult.

With lack of documentation working with your controls is a nightmare.

It would be nice to have a control such as iOS datetime picker
http://www.dosomethinghere.com/wp-content/uploads/2010/11/datetimepicker.png

- and it would be even better if we coulld have a combobox similar to the datetime picker where we have only one scroll to select a perticular text!!

Routing is important for building single page apps which is missing from framework right now. 

Routing component of Backbone is very nice. Simple and intuitive. A library similar to this that is integrated into the core framework would be great.

ASP.NET MVC 4 RC bundle and minimize function useless with kendoui's CSS.
When ASP.NET MVC-s built-in bundling is enabled, kendoui's css-es are broked in the minification.
There are some other miscrepancy between MVC 4 default sites.css and kendoui's CSS-es. 
I'm using 2012.1.322 kendoui version.

 the splash image while loading the web app initially, well, at least for the ios devices.

Combob support for paging would show use the datasource paging settings similar to the grid control and show a label at the bottom as you scroll (Ex. "Displaying 10 of 100 items) and as you scroll increment the items in the list by the configured page size from the datasource.

I want to ask you to add support for this type of call to kendo.format:
    kendo.format('{0} - {1}', [3, 5]);
Of course this is not useful if you have the parameters in seperate variables.
But it is useful if you get the format and the parameters from some external source and that delivers the parameters as an array.

AngularJS, which just released 1.0, is gaining a lot of fans (including myself and my developer-friends). There already is an AngularJS adapter for jQueryMobile, and I hope the KendoUI Team will work on an AngularJS adapter for KendoUI very very soon. I think a solid AngularJS adapter implementation will pull my team over to KendoUI for good.

Development of a Kendo IDE

Has Telerik/Kendo plans to develop its own IDE?  A Wakanda-like IDE, with both design and source mode possibilities, would be very welcome and will give Kendo a real (commercial) boost!

To support various language,
I think KendoUI need language pack system.

Current globalization supports only currency, number format and few label for calendar.

It's so hard to change default english label for buttons and messages.
Sometimes, It's hardcoded in kendo.js file.

It's much better to handle such things in one language file.
Not with individual configuration.

We have a need for a disabled option in the drop down list. I tried it with the Kendo UI dropDownList control, but the disabled attribute was removed in the rendering process.  It is a nice control, but it could use some additional functionality.

http://css-tricks.com/responsive-data-tables/

It would be nice to have a button to see the editor in full screen.

It would be nice if there was an additional dropdown in the Editor that was populated with CSS classes in my .css file.  It would allow users of the application to style articles and other text consistently by simply selecting predefined styles for that layout.  (Hopefully this isn't a duplicate)

It would be great if there are customization of categoryAxis label when ploting has both +ve and -ve values. 
The label need to be settled down at bottom (base line) automatically when there are negative values and same for +ve values.

When hovering over a chart legend item, it would be nice if the underlying series/data item in the chart could be highlighted in a similar way as when the mouse is over the series/data item.

Templates can currently be used in chart labels. It would also be nice if templates could be applied to the chart legend.