But let's be clear, the extended support kicks in at the end of life, a life that does include feature updates so you'd have to count from the end of feature updates, not from the beginning ship date. Also, CentOS for those who aren't going to pay. In any event, as you say, the refresh rate for desktops is 5yrs or so which would bring new versions of the supported enterprise-style OS, one like RHEL which is highly backwards compatible with previous releases