I started working on these features and switching to C++14 would simplify the implementation a lot, thanks to generic lambdas and return type deduction. So I would like to raise the requirement for the final library from C++11 to C++14.
Disclaimer: I was NOT involved in the review, so the following is merely my opinion. There was currently discussion about "switching to C++11" on the list and an often brought argument was "the library maintainer is free to raise the requirement at any time" and "there are already Boost.Libs requiring C++11/14/17". So I assume this change won't be a problem especially as it is C++11->14 (minor change) opposed to C++98->11 (major change) For the rest: As long as you *extend* the interface and not *change* it, there should not be a problem. Additional (reasonable) features to accepted libraries are allowed. Alex