honesty you only dream that any OS has an upgrade path because you are using one that doesn't lie and claims it has.
Ubuntu, windows, etc... none of them can ever be upgraded without a full install. it will kinda work until something will drive you crazy and you succumb to the reinstall. sometimes losing data.
of the rolling upgrade ones, arch was pretty close. gentoo was a crash fest every major kernel or big driver. only time I had problems with arch was even I left one box 3mo without any upgrade...
OSX is a lie like everything from Apple. they call minor upgrades new versions... and every real new version everything breaks and everyone blame the "app" developers. my company IT reimages everyone's laptop when there's a real new version.