Here's one problem: some places will be more popular for pickups and some places will be more popular for drop-offs. Who is going to move the bikes around to balance this?
Likewise, litter of bottles and cans went way down in my home state when they created a 10 cent deposit.
You can also reduce the number of bikes needed by doing timed redistributions. Two people in the same appartment building, one leaves for work around 7 while the other leaves around 9, can share a bike if someone brings it from the nearest subway station to the local bike station at 8.