The Perpetual/Permanent Web on SAFE. (Brainstorming Megathread)

Discussions in NRS Brainstorming sparked a need for this thread.

What are the characteristics and definitions of a perpetual or permanent web (aka permaweb)?

What features/aspects are important to publishers, content creators, and/or clients?

What are the goals of a permaweb and how can they be achieved on SAFE?