I still subscribe to a load of RSS feeds, so blogs are not totally dead. Some might see Hive in competition with sites like Medium, but I think a wider variety of posts are possible. There are loads of people posting about games like Splinterlands and Rising Star. We also have videos from 3speak. Actually playing the games is popular too.
Improving the posting experience is important. It ought to be possible to embed media from more sources. I know it works for a few already, but people don't want to think too much about it.
I can't see the keys system changing much. We need multiple keys for good security and Keychain makes them easy to manage.
Allowing comments from people without accounts would be good. There has been talk of 'light' accounts that would be easier to get. Maybe that will help.
Anything with blockchain will be more complex than Facebook, but we have some advantages apart from rewards. I think we need that critical mass of users for it to take off with lots of good content to attract people. I'm just not sure where that will come from.
Cheers and !BEER