Do you think that the support for C++11 initializer_list is needed (and sufficient). It would probably look like this:

polygon_type polygon{ {{0, 0},{0, 10},{10, 10},{10, 0},{0, 0}} ,
                      {{1, 1},{2, 1},{2, 2},{1, 2},{1, 1}} };

or that we should also provide a chaining tool working in C++98? Which could look like this:

polygon_type polygon = make_geometry<polygon_type>( make_geometry<ring_type>(0, 0)(0, 10)(10, 10)(10, 0)(0, 0) )
                                                  ( make_geometry<ring_type>(1, 1)(2, 1)(2, 2)(1, 2)(1, 1) );

This looks very good, I like this very much. The C++11 too (but I don't yet use that).

Though I like it very much I still doubt if there is wide need for it...
But maybe indeed in some of our own unit tests.

polygon_type polygon = make_geometry<polygon_type>(0, 0)(0, 10)(10, 10)(10, 0)(0, 0) ,
                                                  (1, 1)(2, 1)(2, 2)(1, 2)(1, 1);

With comma operator, hmm, don't know yet. I think we get into problems with multi-polygons (having inner rings too) then? That comma-operator also has nasty side effects w.r.t. preference IIRC (e.g. use it in a ternary-operator...).