IMO, it's important to have a short default period. The vast majority of content - posts, comments, videos, tweets, open source software, etc. will never be registered. It's a huge benefit to get that into the public domain as fast as possible while still providing a reasonable period of exclusivity to creators.
If you're really wedded to the 30 year thing, I think an initial 10 years, and 20 years for the first registered period is a better balance.
