Kendo UI supports PDF export. It would be great if you could add glyph mirroring support to it as well (https://github.com/mozilla/pdf.js/blob/master/src/core/bidi.js). PDF export of RTL languages such as Arabic and Persian need this trick to work properly.

At the moment, the DataSource only uses one field for its ID property (if you enter several, then only one is used, apparently).  This doesn't reflect reality, in that in many cases (where one record is a child of another), the key field for a database table is a composite (from 2 or more fields).  
The existing situation causes problems in inline editing of the KendoUI grid, because default values need to be set for foreign key fields, but if these are set to a valid value, then spurious calls to the Inline_Create method occur because the DataSource treats the record as a new record when it is not.
In any case, allowing multiple fields would simply reflect reality.

Please think the Kendo UI validation farmework not only in terms of client-side validation but also in terms of reporting server-side errors.

A framework that would only provide a way to display a validation error message based on a client-side rule after each related input field would not be very helpful in my opinion.

All errors need to be reported in a consistent way. My preferred option is:
- a message box at the top of a form to display all messages including OK messages and error messages (client-side and server-side).
- higlighted fields with tooltips (not to clutter the form layout) to repeat error messages in context when applicable.

Although the framework built into Kendo UI might only provide client-side validation, please make sure to provide entry points into the UI used to report errors. Alternatively, leave the UI to the developer and provide a simple way to collect all validation error messages on a form.

Add ability to pass dynamic parameters for load on demand tabs - 
similar functionality to the DataSource Read Data option which allows additional parameters to be returned via a javascript function.

Today you can only export JavaScript primitive values - String, Number, Date, Boolean.

http://www.telerik.com/forums/export-grid-to-excel-cells-with-hyperlink

Add a new Kendo UI component to display a record vertically (Or add an option to the existing grid to change the orientation of the records).

Usually, I was using vertical grid to display a single record but some people might need it to display more than one record (ex: when you compare items on best-buy web site)

The vertical grid could also be used as a property grid (http://www.telerik.com/products/silverlight/controls/propertygrid.aspx).

Add marker clustering support to the Kendo UI DataViz Map control.
If you are viewing a map with many markers nearby, they should group together so that the map is more pleasing to the eye.

This functionality already exists in the Telerik Silverlight Map control and it would be great to see similar functionality here.

Here's an example of what I want: http://demos.telerik.com/silverlight/#Map/Cluster

Suppose a model is defined with settings for editable, required, validation, etc. Then this model is used a datasource's schema.

Instances of the datasource's data will be models. However, if a model is bound to some HTML view, it's settings are not applied to the view. All settings have to be manually applied to the HTML elements.

I suggest that these settings are applied automatically. Then for example, a field's property like "required" wouldn't have to be coded at two different places.

There is an option to freeze the left most column of the Kendo Grid by setting the lockable property.
But this is limited to the Left Hand Side columns only and there are no ways suggested to freeze the Right Most columns.

See this Kendo Forum post:
http://www.telerik.com/forums/multi-select-in-responsive

In short, we need additional approaches to grid multi select using touch events

In horizontal configuration, with resources displayed down the left side of the control, a large number of resources will cause the control to stop functioning.  In some cases, like ours, we do not have the option to filter the resources by those that have scheduled events, and so infinite scrolling is necessary for the number of resources we need to support. For reference, see the forum post about this here: http://www.telerik.com/forums/virtual-scrolling-for-scheduler-with-many-resources

As per the .NET format support shown here:
http://stackoverflow.com/questions/11731996/string-format-numbers-thousands-123k-millions-123m-billions-123b

And here:
http://msdn.microsoft.com/en-us/library/0c899ak8%28v=vs.100%29.aspx#SpecifierTh

123456789.ToString("#,##0,") will return "123,457".
123456789.ToString("#,##0,K") will return "123,457K".

kendo.format("{0:#,##0,", 123456789) will return "123,456,789".
kendo.format("{0:#,##0,K", 123456789) will return "123,456,789K".

As per the .NET standard, each trailing comma will round off 3 digits, so 123456789.ToString("#,##0,,M") will return "123M".

I have experience with OpenText Brava Enterprise. I've had the chance to integrate their Viewer in our in-house document management system. This viewer opens up to 100 file formats and allows to add/remove/edit annotations on files and saves these annotations as a separate layer on top of the file. So next time you open the same file to view, you can load the annotations (via API) calls and place the layer of annotations on top.

I was hoping I would see the same thing with Telerik PDF Viewer (and I am aware this works only for PDF). To allow the user to add a Text comment, Shapes, Stamps, Image, PDF Bookmark, etc.

Ability to change a treeview node's description (node text) inline on the fly

Go here: http://demos.kendoui.com/web/tooltip/api.html

1. Click on Area 1 or Area 2 
2. Then:
a. click outside tooltip area
b. press "Esc"
c. scroll down the page

Current result: tooltip is closed

Expected result: tooltip should not be closed

It would be great to configure tooltip hide behaviour whether to close or not on 2. a, b, c actions.

A quarter is not the same as 3 months in the same way that a week is not the same as 7 days. Feb-Mar-Apr is not a standard quarter. Kendo automatically lines weeks up on Sundays. Please consider doing something similar for quarters.

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

Add capability to upload .mpp file and populate the GanttDataSource, GanttDependencyDataSource and Resource Assignments. Thanks.

What about adding dynamic scrollbars to the HTML5 Diagram widget?

As developer I'm familiar with the pan and zoom concept, but customers and normal users are expected to see scroll bars to move around a diagram. 
In this demo

http://demos.telerik.com/kendo-ui/html5-diagram-sample-app

you can add objects that fall outside of the main view, but no scroll bars appears.

Here http://kendoui-feedback.telerik.com/forums/127393-telerik-kendo-ui-feedback/suggestions/6552432-html5-diagram-control-allow-scrolling

was posted a similar request, but the scrollbars Kenshin suggested 
are static.

The scrollbars does't readapt if the work area changes. 

If you move objects around, apply a different zoom, add more elements, and so on.

Please add option for setting custom window titlebar icons like in this Telerik MVC Window example:

http://demos.telerik.com/aspnet-mvc/razor/window/loadingexternalpage