There's also the challenge of getting all the stations set up as Customer Service Outlets, otherwise there will be a lot of problems with people unable to buy Presto cards, unable to set up child/student/senior fares or unable to clear negative balances.
You can buy Presto cards at vending machines--they are currently in a few subway stations, and the TTC has stated that every subway station will have Presto vending machines in 2017. So you don't need a CSO to sell cards. Plus, you can order them online and get them mailed; but as far as in-station, I see no reason why a vending machine can't suffice.
Same for negative balances--you can now clear negative balances at the Self-Serve Reload Machines, which are also going to be located in every station. You can also clear negative balances by loading online. This was not previously the case, however they made it possible in an update quite a while ago.
The only thing that will need human intervention is setting up concessions. However, for children, high school students, and seniors, that will only need to be done once, since they set the expiration date for when you turn 13 as a child/20 as a student and have no expiration date for seniors, for obvious reasons. With children requiring 1 visit when they get their card, and just one more visit when they turn 13 to move from child to student, and seniors needing just one visit period, I don't think you need every single station to be a CSO. I think having davisville, and GO stations, is sufficient. Not sure what the official plan is regarding that.
Post-secondary students currently need to be re-validated every year as it stands for the metropass, and that will presumably continue with Presto--however, that is currently only done at one station, Sherbourne, so similarly there is no need for every station to be a CSO for postsec.