> bounded::integer uses built-in integers as the template parameter to determine its bounds. This means that it cannot store an integer larger than ...
They say the limitation arises from using "built-in integers" as template parameters. It is reasonable to assume "built-in integer" means "int". It is more a stretch to assume "built-in integer" means any number of types depending on the evaluation of several ifdefs [which is what I found in the source].
There is nothing about a "use case" relevant to any of that quoted statement, so I find your reply very confusing too.