Note that the html5 number input type provides less functionalities (formatting, separators, events ect) than the RadNumericTextBox control. Therefore redesigning of the control and make it input with number format will cut a lot of the functionalities that can be currently used. As I said our dev team is deeply investigating all the possibilities in this matter and will do their best to apply such functionality if possible.
For now you can set html5 input type to the RadTextBox and in case it is set to "Number" the required number keyboard will appear in mobile device.
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