The Kendo UI is using the version of the Bing maps which is passed based on the bing key.
Changing the versions should not affect the Kendo UI Map functionalities. The "Bing Maps SOAP Web Services API is superseded by the Bing Maps REST Services API" and the Map widget is using REST services.
Please have in mind that as the version 8 is a new product, it can still cause an unexpected issue, which can be fully tested when the version 7 is stopped.
Still, if any unexpected issues occur after using version 8, please let us know and we will gladly assist.