Armadillo 15.0.* now makes C++14 the minimum compilation standard. For most packages, adapting to it can be very simple, and yours is one of them. As your github repo already has CXX_STD=CXX11 commented out, all we would need for it to be part of the transition is a new upload to CRAN. I verified that it builds just fine without imposing C++11, and I am sure you are aware too.

In any event, please see issues #475 and below for context, and notably #489 for this first wave of PRs. It would be terrific if you could make an upload to CRAN 'soon' to remove the reliance on C++11 which we needed in the past, but which is by now a hindrance. Please do not hesitate to reach out if I can assist in any way or clarify matters.