Use correct status for "proposed" extension

Author: Pennycook

sycl/doc/extensions/proposed/sycl_ext_oneapi_named_sub_group_sizes.asciidoc

@@ -51,12 +51,11 @@ This extension also depends on the following other SYCL extensions:
 
 == Status
 
-This is an experimental extension specification, intended to provide early
-access to features and gather community feedback.  Interfaces defined in this
-specification are implemented in {dpcpp}, but they are not finalized and may
-change incompatibly in future versions of {dpcpp} without prior notice.
-*Shipping software products should not rely on APIs defined in this
-specification.*
+This is a proposed extension specification, intended to gather community
+feedback. Interfaces defined in this specification may not be implemented yet
+or may be in a preliminary state. The specification itself may also change in
+incompatible ways before it is finalized. Shipping software products should not
+rely on APIs defined in this specification.
 
 
 == Overview