Im currently developing an large extension using extbase and fluid.
Today i did some performance checks with xdebug and kcachgrind and i
figured out that 30% of the rendering time is spend in the function
TypoScript::convertTypoScriptArrayToPlainArray i head a look on that
function and saw that it copies the hole array and converts it. The
array is passed as a copy to each recurive call. The attached patch
extends the testcases to have a more solid base for refactoring and give
an approach to refactor the method in a way that no copying between two
arrays is needed.

But in general i what to ask? Why do we need to transform the whole
typoscipt before the extension is rendered. This can even be done by an
accessor object at runtime(with a caching layer)