It will be very nice if the AutoComplete, DropDownList, ComboBox, and MultiSelect components have the floating label functionality like the TextBox widget 

A kendoDropDownList places an arrow to the right of the <select/> element, indicating it's a dropdown (.k-i-arrow-s). It would be cool if kendoMultISelect did the same thing. 
Clicking the <select/> element or the arrow should also toggle the visibility on the list items.

See http://stackoverflow.com/questions/31825788/kendo-multiselect-to-have-arrow-icon-and-behavior-to-close-on-click .

Check out this idea. It may help solve this issue and help with UI presentation.
http://feedback.kendoui.com/forums/127393-kendo-ui-feedback/suggestions/3767009-treeview-in-combobox

Admin edit: A Knowledge Base article that shows how you can achieve this: https://docs.telerik.com/kendo-ui/knowledge-base/disable-multiselect-items

Users wonder why the filter has not been removed from the dropdownlist when they use a browser's text INPUT[X] to delete the filter. The browser raises no event is raised when the X is clicked, and so the list does not revert to the unfiltered list. Users must hit the Delete keys on the keyboard. Although developers can use CSS to remove the browser's [X], it would be more convenient if kendo could do this by default for the dropdownlists's filter box, so that developers would not have to remember to add the CSS every time.

Currently it is not possible to show the filter row until some data has been received and the dropdown is visible.

Please enhance/change the DropDownList widget so that it will be possible the enter a filter expression before any data is queried.

Related forum post: http://www.telerik.com/forums/server-filtering-how-to-not-query-data-until-filter-has-been-provided

Not showing the selected items externally , only within the drop down.

The default behaviour of select elements is to open up with a space-keypress when the elemented is selected (focused). 

New control ComboBox with CheckBoxes

Currently when you enter custom text (referred to as custom value) the control sets the text entered as both the TEXT and VALUE.

I suggest this should operate like the Telerik ASP.NET combobox which only binds custom entered text to TEXT and null as the VALUE.

This then allows you to differentiate between an item selected from the list and one entered.  When you call text() it would return the selected item text or custom text entered and value() would return the selected item data value or NULL if custom text.

Fast and responsive UI rather then flaunt and animated. 

I have played for a while with the demo of the components.
What I noticed is that components with popup elements, such as ComboBox, DatePicker, TimePicker, ... have a small but visible delay, which becomes quite annoying with time.

Look at ComboBox demo, it seems there is some delay due to pre-configured animation effects on the control.  In slower browsers (take Firefox 6.0.2) the delay is obvious. 
The support for animation in general is a cool idea, but in most business applications it is not welcome by users who use application on a daily basis. 

Personaly, looking at the demo I am not sure if I can rely on kendoUI if my application designed for "do the job" rather then "enjoy UI".

I think it would be very nice if the demo has settings to disable all animations, to run it at full speed and demonstrate rich AND really responsive UI.

In order to check dirty tracking, I would like to check the defaultSelected of the option of the MultiSelectControl. This now does not work.

Currently, the AutoComplete widget supports only a single separator value. It would be desirable to be able to fire an autocomplete action after multiple separators, which can be suplied as an array in the separator property of the configuration object.

Currently multiselect control has a change event only which is supposed to take care of add/remove event.
Please add proper events or pass info in the change event about what changed, so that developers doesn't have to write the same JS again and again.
See OnaBai's reply here

http://stackoverflow.com/questions/16608565/kendo-multiselect-trigger-an-event-when-an-item-is-removed

http://stackoverflow.com/questions/17653958/kendo-ui-multi-select-remove-selected-element-using-value

The autocomplete inorder to support search and at the bottome display all the results and the number of matched results,
there is need to footer template, like the facebook search autocomplete.

Right now other JS UI libraries allow the autocomplete dropdownlist to dynamically size based on the returned content. KendoUI sets the width to the width of the input box. I understand this looks nice but doesn't work for all business aspects. An example is my company needs to enter search criteria but the return results is the code and description. Since this can get longer than the input box the text is wrapped. This confuses users as they don't know where one item starts or ends. We use to modify the source files to fix this but the Q2 release changed a few things and stopped us from doing this.

The grid and autocomplete widgets really need no-data templates which display when the returned data is empty. The MVC controls were pretty good at this.

The option to allow new items to be added to the list, as opposed to items exclusively in the datasource.

For example see this: http://jsbin.com/iXEtonO/4/edit, only built in

When using IE10/11, it natively supports the clearing of input element so essentially when hovering over a Kendo ComboBox with a selected value, this is the end result:

http://i1256.photobucket.com/albums/ii484/vobreshkov/KendoComboBox_IE.png?t=1376577876

I am constantly getting requests to have such way (or adding an extra menu item) to my combo boxes to allow users to click on something and clear the selection. Please consider extending similar functionality to the combo box that is available on all browsers.

There are a couple of things that are very common that I would like to add buttons for.  The first is for clearing the value and the second is a + for adding new items to the list.

The + button is an important one from a usability standpoint.  Quite often the combo/dropdown is populated from a list that is managed on a separate page.  It is too cumbersome to have to use stop entering and go to the admin page to add the new item and then come back to add whatever they were working on previously.

I know I could simply add a button beside the widget but this just doesn't look as nice as it being built in.

Currently it seems that kendoDropDown only supports select elements with options and not optgroups. Would like to see this widget support select elements with both optgroup and option elements.