DPC++ already supports intel::max_work_group_size but though the documentation for the attribute specifies the behavior at SYCL level, the attribute does not have a related SYCL extension detailing the behavior. Such an extensions should be added.

Additional options for this extension specification:

1. Allow 1-3 arguments in the attribute and add the requirement that the kernel must be launched with the same dimensionality as the attribute. This makes it in line with other SYCL 2020 core attributes for work groups (sycl::reqd_work_group_size and sycl::work_group_size_hint). See discussion [SYCL] Change sycl::reqd_work_group_size with optional dimensions #7450 (comment).
2. Add new sycl spelling, i.e. sycl::max_work_group_size.
3. Add a kernel compile-time property analogue. See https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/experimental/sycl_ext_oneapi_kernel_properties.asciidoc.
   ** Note: Since this would be experimental it may have to be in a separate extension.