For now SYCL comes with a CL/sycl.hpp header file that defines all the SYCL entities under cl::sycl:: namespace, which makes sense for SYCL.
But if we want SYCL broader and more general than just OpenCL, it makes less sense now. See for example https://github.com/illuhad/hipSYCL or some embedded systems.
So this extension propose to have another sycl.hpp header that declares all the SYCL entities under sycl:: namespace.
A side effect is that with this SYCL extension we save typing 4 characters for each fully qualified entity. :-)