Do you know if Optimizely Free Account will end by the end of 2016?
As far as I know, there is currently no plans to end access to Starter accounts at the end of 2016. However, with that being said, since these are legacy accounts this could change in the future. I'm sure if that were to happen you would receive notification of such a plan change.
Please feel free to reach out if you have any additional questions or concerns.