I'm probably not the best person to answer about this. I believe that the 7 day limit is imposed because of technological reasons, i.e. if ALL existing posts are included in every payout calculation, the computational cost of the calculation essentially grows without bound. I believe other solutions are in the works, and changes to the payout structure are always being considered (there is a big change coming on Tuesday which has been slightly contentious, although the witnesses pretty much unanimously support it). The platform is still 'beta' apparently, although I have no idea how long that is going to last. In terms of the business model, I guess Steem does have a market cap of $500 million, so I don't know if I would call it a weak business model. Consider the examples of Facebook, twitter, reddit, etc... Personally I would rather have the opportunity to receive a single payout for my content than no opportunity. Also, it's important to recognize that the Steem network has much greater applications than simply the Steemit website. The Steem network is a blockchain with zero transaction fees and nearly instant confirmations. If you wanted to build a traditional platform like Twitter on top of Steem that allowed monetization and included opportunities for traditional ad revenue it is possible, although you would probably be better off waiting for EOS for that.