SP will be needed for those that want to stay engaged and honestly this might be a good thing to a point. I think that Steemit could offer some sort of a RC/Mana boost for 90 days to allow people to test the waters and see if they like steemit. After that over the following 90 days the amount of free RC's/Mana drop off and people would have to either buy SP or Lease it to be able to keep functioning.

The important thing to remember is that steemit works best long term if people are powering up, but pulling Steem out of the system and selling on the open markets. If someone is just trying to earn a few dollars a month off rewards and not willing to power anything up they no longer will have a place on steemit.

This will all sort itself out in the end.