For consumer products, a seamless authentication can really boost the usability of the app. In the centralized world, 'Login with Facebook' standardized the login experience. In the decentralized world, more specifically dApps built on EOS blockchain, will Scatter or any other dApp become the defacto login mechanism? Or would each dApp have to generate their own public-private keys for their users like Steem/Steemit?
dApp's generating their own private keys for each user is not a viable strategy. Users won't want to hold many of the keys as it's stressful and are objectively harder to memorize than a typical username/password combination.
A more likely future to the above - but by no means a good solution - would be for users to generate a new public/private key for all secondary accounts and enter it onto sites like you would using myetherwallet (MEW). The risk would be lower as the secondary account would likely hold no EOS but just act as an account authorizer.
Anyone familiar with IT security should already see the link here between how users will make one account name / password combination and use it across multiple (if not all) sites they use. This is a discouraged practice as one account being hacked compromises all of them but yet users still do so because it's practical.
For the above reasons I hope Scatter (or a competitor to them) will become the standard, we should learn from the early web and make things better, not the same.