My bad, yes, I do have BOOST_GEOMETRY_IMPLEMENTATION_STATUS_BUILD defined.
I think that this MPL_ASSERT should be removed and replaced by

    MPL_ASSERT((is_implemtented<bla, bla>))

right at the begining of the algo free function.

That would make possible the implementing of a "runtime" (vs compile time) version of the free function. But that I would like to discuss "Runtime specified geometries" thread of the mailing list.

IMHO this is_implemented<...> metafunction is so important that it needs to be available outside the doc status tool. I'll try to push a better implementation later today.