The verdict of the review was to merge double_ended into container - a wise decision. However, it'd require the original c++11 library to be converted to a c++03 library - I didn't have the taste for that. I'd solve this by declaring Boost.Container to be C++11 and include Double-Ended in it. It's almost a decade since its publication so even conservatively taken it is "old enough" to require it. And library maintainers are free to do
that.
I apologize for not having spotted that. You possibly read, what I was willing to consider to do, yes, a very good reason to drop your tools. In 2020, writing C++14 has become painful in hindsight, i.e. not a very good invest of time, support C++03, anything other than the latest really.
True. However I'm quite happy with C++14 so far and having to resort to C++11 then is not that hard unless you need constexpr all they way down and up. And IMO Boost should provide extended support for older standards. So I'd recommend going from C++03 to 11 or 14. The latter might be an issue with older MSVCs which lack behind in 14 but are quite complete in 11. But well...