So, I'm not an expert, just a guy who is interested and trying to answer the same question as you. Basically, there will be many similarities to Bitshares and Steem, just more general. So, the system will be delegated proof of stake, which means (as far as I know) that only the witnesses are actually running the full EOS blockchain. Then many different users who are interested in specific apps (like Bitshares or Steem) can run significantly reduced code on their computer that interacts with the blockchain, but only with the data from the app they are interested in. That's my naive understanding. I need to learn more.