Key points: No impact if you plan to stay with Solo AP or ZoneDirector managed use. But APs with old certificates (only) will have problems communicating with SmartZone controllers after November 27, 2016 if they do not get a certificate refresh. Most newer APs have new certificates, but running an SZ version with refresh capability (export .res file, import .req file) can update an AP.
Latest ZD code can also identify APs with only legacy certificates, but not update them. This is offered for customers who may eventually migrate to SmartZone (and should install a vSZ-E and update certificates now).