The first OS to drop 32 bit support, thus eg fixing the year 2038 problem the easy way. Not sure if any others will though, at least not until arm64 is more widespread.
The first? What about Windows Server 2008 R2? Or PC-BSD 9.2?
Last time I checked, they were mostly a FreeBSD distribution with a bunch of user friendly sugar coating on top (an easier package manager, default installation includes a fully configured desktop environment, ...)
I don't mean that as a bad thing - I used PC-BSD for a while and it was great. Not everyone needs to reinvent the wheel and reimplement drivers etc. But I see it more as a distribution of an OS than an OS.