It’s well documented on the VMware Product Lifecycle Matrix that on 24th August 2016 vSphere 5.0 and 5.1 general support will end, moving into technical guidance.
Way back on 21st May 2014 VMware moved vSphere 4.x into ‘end of general support’. Then a few months later on 15th August 2014, VMware removed the ability to download, downgrade or generate new license keys for vSphere 4.x see VMware KB2039567. This essentially meant that you couldn’t expand your unsupported hypervisor environment.
So the question is how long until VMware remove the ability to download or generate vSphere 5.0 and 5.1 licenses?
VMFocus 
It’s 5.x licenses not 5.0/5.1.
5.5 is still supported for 2 years.
5.x is 5.0, 5.1 and 5.5. Whereas I refer to 5.0 and 5.1.
Same license for all 3 versions.