Now autocomplete can not use to suggest email input, just like I input my name, the widget can show myname@xxx1.com, myname@xxx2.com, myname@xxx3.com like this, and the data will be only [{"email":"@xxx1.com"},{"email":"@xxx2.com"},{ "email":"@xxx3.com"}]

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

Hi Support Team,

Current, we are facing a problem when using "kendo ComboBox" and options in attachment. To reproduce this issue, you have to run sample(kendoui.web.2013.1.319.commercial\examples\web\combobox\index.html) from attachment on safari of iPad.
Step by step:
1. Click on arrow icon to expand items
2. Click on textbox
3. Type data to search items near the last item on textbox

Actual: ComboBox don't auto scroll to item of user typed.

Best practice dictates that dropdowns open on mousedown, such that that user can press, move to the desired item, and release all in one movement. You'll of course find this behaviour across many apps and OS's, including MS Office, Windows and OSX. Sadly, Kendo UI dropdowns open on mouseup/click, rather than mousedown, which means the user has to do two clicks to get to what they want. For heavy-usage applications, this is a big pain for users, and definitely affects usability.

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

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.

New control ComboBox with CheckBoxes

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.

When bound to oData, the autocomplete contains filter should treat each WORD as a new "substringof"....or make a new odata advanced contains type\property.

This is more what users expect when searching...and the odata spec has it covered.

http://www.kendoui.com/forums/ui/autocomplete/odata-google-like-filter.aspx

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.

I'd like to be able to style the matching text from autocomplete, so I'd like the option for kendo to perhaps wrap the text in a span or something I can get a handle on...

So if I typed "Back" it'll give me results like this
<li><span class='t-match'>Back</span> to the future</li>