Add "scriptability"
It would be useful to be able to "script" how Kiosk manages e.g. windows, e.g. assign that a specific window should have a certain position, be available only on a specific monitor, have a specific size, etc.
It could be done in a declarative manner, e.g. a yaml file with rules, or by integrating a scripting language. The former is probably more maintainable, while the latter would provide more flexibility.
A potential approach is to start with the former, and down the road if it is not enough, try the more flexible approach on top.