Security updates to Win7 will be free until Jan 14, 2020, they are ending free non-security updates and phone support on Jan 15, 2016.
Very few applications that came standard in Win7 will not be supported, but only one, IIRC, will be removed during the upgrade. (WMC)
The only really big thing is DX12, which for a gaming rig is something to seriously consider. If you can live without WMC, and most people can, upgrading to Win10 would be a good thing.