People are being scared off by the experimental status on https://gcc.gnu.org/projects/cxx0x.html
e.g. https://gcc.gnu.org/ml/gcc/2015-10/msg00025.html This makes it clear C++11 in 5.1 is no longer experimental. We also have a "Standard Conformance" section for G++ in https://gcc.gnu.org/bugs/ which says "Two milestones in standard conformance are GCC 3.0 (including a major overhaul of the standard library) and the 3.4.0 version (with its new C++ parser)." I've added some more recent milestones, although maybe std::lib conformance doesn't need to be mentioned in this context?
Index: htdocs/projects/cxx0x.html =================================================================== RCS file: /cvs/gcc/wwwdocs/htdocs/projects/cxx0x.html,v retrieving revision 1.67 diff -u -r1.67 cxx0x.html --- htdocs/projects/cxx0x.html 26 Jan 2015 11:12:43 -0000 1.67 +++ htdocs/projects/cxx0x.html 6 Oct 2015 10:58:01 -0000 @@ -28,10 +28,10 @@ line. GCC 4.7 and later support <code>-std=c++11</code> and <code>-std=gnu++11</code> as well.</p> - <p><strong>Important</strong>: GCC's support for C++11 is still + <p><strong>Important</strong>: Before GCC 5.1 support for C++11 was <strong>experimental</strong>. Some features were implemented based on - early proposals, and no attempt will be made to maintain backward - compatibility when they are updated to match the final C++11 + early proposals, and no attempt was made to maintain backward + compatibility when they were updated to match the final C++11 standard.</p> <h2>C++11 Language Features</h2> Index: htdocs/bugs/index.html =================================================================== RCS file: /cvs/gcc/wwwdocs/htdocs/bugs/index.html,v retrieving revision 1.116 diff -u -r1.116 index.html --- htdocs/bugs/index.html 5 Jul 2014 21:52:32 -0000 1.116 +++ htdocs/bugs/index.html 6 Oct 2015 10:58:01 -0000 @@ -696,9 +700,12 @@ However, some non-conforming constructs are allowed when the command-line option <code>-fpermissive</code> is used.</p> -<p>Two milestones in standard conformance are GCC 3.0 (including a major -overhaul of the standard library) and the 3.4.0 version (with its new C++ -parser).</p> +<p>Significant milestones in standard conformance are +GCC 3.0 (including a major overhaul of the standard library), +the 3.4.0 version (with its new C++ parser), +4.8.1 (complete C++11 language support), +5.1 (complete C++14 language support), +and 5.1 (complete C++11 and C++14 standard library support).</p> <h4>New in GCC 3.0</h4>