Currently we ship shiboken as part of the PySide2 package.
This inflates the wheel size by quite a bit.
For instance on macOS:
shiboken size - 4MB
libclang.dylib size - 64MB (51MB on Windows)
The report sizes are for libclang 6.0. For 4.0 on Windows the size is ~22MB.
We would save a bit of space in the wheel if we would ship shiboken as a separate package.
An additional step would be linking against a static version of libclang, thus reducing the size further.