What are the key reasons someone should go to Steem rather than to some existing social platform? Steem will likely be slower and the barriers to contribute will likely be higher.
Secondly, do you think it is a good basis for building communities if everything is associated with monetary rewards? Sites like Reddit are exactly enjoyable because, most of the time, reward is only imaginary, just like in real-world gatherings of people: It is about having a good time rather than about an exchange of money.
Thirdly, how do you ensure that the things people post on Steem are their own work, especially if the data is hosted elsewhere, e.g. on YouTube. There will probably be massive, irreversible thefts of intellectual property (a.k.a. reposters, but with actual money involved). Conversely, a lot of valuable content comes actually from reposting and "karma theft" (which is what linking e.g. a blog article from someone else actually is).
Fourthly, how do you avoid fraud as for example often found on Kickstarter? Kickstarter actually has a review process and even they are not fully equipped for it. I am not seeing reliable moderation ever scale enough such that it can withstand the likely immense fraudulent interests due to the monetary incentives.