This appears to be languishing.
If this is languishing because there's a concern that this will break applications that request 4.4 and don't actually need ARB_buffer_storage, I will offer the following points:
(1) not adding this commit will break applications that *do* need ARB_buffer_storage. There's no evidence of which group is larger, but persistent mapping is not exactly a corner feature of the language;
(2) even if some applications are broken in new wow64, there is still a simple workaround—viz. use old wow64;
(3) currently *all* d3d applications are broken in new wow64, because if wined3d is told that ARB_buffer_storage is available then it will use it; however, wined3d is perfectly capable of doing buffer updates using non-persistent memory, even for the most recent d3d versions (potentially at a significant loss of performance, but this is still better than failing to render at all);
(4) fixing this the "right" way requires adding a new extension, which is a slow process and, moreover, will never be universal, so we will need this anyway.