I know that Swing has its own mechanism for borders lazy initialization. It works well when you know what border goes where from the beginning. For example if you know that all of your buttons have a gray line border with 1px width by default - you can set its settings just once using BorderUIResource.LineBorderUIResource. It will be then used in each button UI instance as a border source.
The problem here is that almost all of borders used in WebLaF are calculated in runtime when the UI is installed or updated. Update might happen at any time - for example when some of UI settings are modified, or default style has changed (styles manager coming a bit later, just telling about it ahead). In this situation updating a border created from a lazy value will be a real pain and also makes that lazy initialization useless.
Also soon enough it will be possible to set your own border that will not be replaced by WebLaF border. From the inside - component UI will create an additional border that will combine L&F empty border (that is used for proper margins) and your custom border and will simply keep WebLaF border updated.
These are the reasons why i am not using default Swing borders lazy initialization mechanism.
I guess your suggestion was about the problem that WebLaF doesn't clean up some of component settings it modifies (including borders)?
If so - i am still working on that problem and will be adding fixes for various UIs so that WebLaF won't leave any traces after uninstallation.