Currently kendo.DataSource.get() and kendo.Datasource.getByUid() methods are very slow in case there some non-trivial amount of data stored. Actually, these methods loop on all items in dataSource on each call.
Why not add index for id field? Indexed access can boost up many real-life scenarios.
I prepared following jsfiddle to demonstrate the slowness:
http://jsfiddle.net/terikon/eb3tsjzf/9/