Which, as I said, would be at least another year away.
My response was to you bringing up the topic of security so I simply addressed that with details of Ubuntus LTS. Other than that there would be no reason to upgrade however even then you could update any software package found to have security issues on an individual basis through PPA, debs or source. That is the flexibility of opensource.
No operating system can be supported forever but funnily enough Ubuntu have just announced an extension to 5 years for 12.04 LTS.