As far as I can see there is no replacement for den Converters and the ConverterFactory in Vaadin8.
Converters and the ConverterFactory were very nice features that we used a lot in out Projects. It was an easy way to make sure that complex object are rendered always the same. You didn’t need to think about it if you used an object as an item in a combobox or as a column in a grid or table. It just looked fine.
In Vaadin8 you need to use the ItemCaptionGenerator for ComboBoxes and Renderers for Grid to do the same. But you have to add the generator and renderers every time you use a complex type. This is pretty annoying.