If possible, please consider making the Kendo DataSource compatible with the data returned from using an ASP.NET MVC 4 Web API project possibly by adding a 'webapi' dataType.

Add sort/filter events or add an extra parameter in the 'change' event object so that we can detect if a data source was filtered or it was sorted.(Mostly needed when working with grids)

There has been many scenarios where I've needed to know when a DataSource finishes a "read" or "sync" operation.

I know there's the global "sync" event that I can bind to, but a lot of the time I only care about the result of one specific sync call. I can use the "one" method to only listen to it once, but this complicates things when I also care about errors. Since I need to register callbacks for both the "sync" and "error" events, and then unregister either one or the other, depending on which event fired.

It's even harder hooking into a "read" event because the DataSource doesn't expose one. I know I can hook into the "change" event of the DataSource, but I still have to guess whether the change event was fired because of read, or because of some other change.

If these methods returned a deferred it would be a lot easier to handle the circumstances where an app needs to do additional things after a "read" or "sync" is completed.

Option to refresh one item from a datasource from the server using a GET request using the transport read url appended with the item ID field value.

See: http://www.kendoui.com//forums/framework/data-source/how-to-refresh-an-item-in-a-datasource-with-server-data.aspx

dataSource: {
       type: "odata",
       typeversion: "3"
}

Add support for Web Sockets to enable push notifications to grid, listview, and other data bound widgets.

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.

Possibility to add filters to hierarchical datasource, that execute recursively.
Use case: In TreeView we need to search for some element text, we need to see elements that contain some text and their parents expanded. Filtering could be usefull here.

Though KendoUI already has an MVVM style binding, it would be much better to have a css binding allowing us to set class on HTML elements based on arbitrary conditions.

Just look at the Knockoutjs css binding.

Add a visible property to the column items for the grid control. Then provide the value in the view-model. This would allow us to declare the columns in html and manage their visibility in the business logic.

This feature was already requested in another post, but it was missunderstood. (http://kendoui-feedback.telerik.com/forums/127393-kendo-ui-feedback/suggestions/11578722-support-sorting-datasource-groups)

The idea is to allow for Groups in DataSources to be sorted in ways other than alphabetically; this will allow for certain groups to be given priority.

Add support for automatic polling/refresh on DataSource.
Property: interval in milliseconds

signalR gives the possibility to quasi direct connection to the server side with easy parameter passing and easy implementation.

"WebAPI now uses the DateTimeOffset time as a main type when it comes to dates. However DateTimeOffet requires the Model(that the dataSource creates) to keep information for both Date and Offset which is not possible with the current architecture of the DataSource and Model of Kendo." Based on http://docs.telerik.com/kendo-ui/aspnet-mvc/helpers/grid/how-to/oData-v4-web-api-controller
Please add full support, also when working with Dates. Thanks.

Right aligned columns are common for number fields and it would be nice to simply set a property in HTML and/or the view-model:
E.g { "field": "amount", "align": "right", "title": "Amount", "width": "110" }

It'd be terrific if there was built-in access to client-side data stores (e.g. IndexedDb).

Replace the current implementation of ObservableObject/ObservableArray with the new js features Object.observe/Array.observe.

We need an option to make the datasource immediately drop the current in-flight data fetch request if another one comes in.

Currently, if the user clicks around several times in a row changing grid datasource parameters too quickly, several requests get fired off, but the grid waits for the very first request to complete before issuing the next one. This makes the user's wait time twice as long and also makes the grid content appear to switch back and forth as requests complete one after another. Very unpleasant effect.

Mobile app should be able to save the data locally in the mobile device and  when online network status is detected, should have the mechanism to synchronize the local data back to the server. I asked this during the webcast demo about supporting the html5 local web storage or the html5 indexeddb.

We are evaluating migrating from Asp MVC to KendoUI (MVC), which looks promising. However, there is one BIG problem we have encountered: 

Cell values of null are displayed as "Null" instead of as ""! I really urge you to change this since this would require large changes to very many places otherwise. At least an option to select the behaviour.

Thanks
/Victor