One of the ideas that has been tossed around is having some sort of investor-VESTS that would not have content voting rights (nor earn curation rewards) but would instead benefit from some higher interest rate (equivalent to lower inflation). This would mean that only actual social media users and not investment-motivated holders would be curating and earning curation rewards. 

I think this is probably a better solution than curation guilds because even _choosing and monitoring a guild that is doing a good job on curation_ is something that many investors are probably not interested in doing and won't do very well. There are some very tricky issues with making this work though.