Is PPD8 still in effect? If so, has it been recently modified or otherwise changed? Is it still relevant/effective?

PPD8 is still in effect in terms of there now being a plan. The directive was meant to coordinate agencies and deliver a national preparedness plan that was born out of multi-agency cooperation.

The Assistant to the President for Homeland Security and Counterterrorism shall coordinate the interagency development of an implementation plan for completing the national preparedness goal and national preparedness system. The implementation plan shall be submitted to me within 60 days from the date of this directive, and shall assign departmental responsibilities and delivery timelines for the development of the national planning frameworks and associated interagency operational plans described below (Homeland Security, 2011).

My understanding is that it is still in effect because it is now a completed plan.

References

Homeland Security. (2011) Presidential Policy Directive / PPD-8: National Preparedness Retrieved