I previously posted about the idea of enabling upvoting for off-chain content, for example a YouTube video or Substack newsletter post. A fully-featured implementation of something like that could have a new type of blockchain transaction different from a post which doesn't participate in the author rewards the same way (since the author wouldn't be on the chain) but could participate in curation rewards. At the frontend side, Steemit could add RSS reader functionality so you can easily upvote content you already tend to engage with.