1 bike -> 1 post. There isn't enough posts for all the bikes.

The stacking problem could be trivially solved by adding a small explosive charge that ejects your bike sideways when needed.

I guess it is, but it would be by using the lock as designed, rather than by being careless.

Either you have one bike per post, which is not efficient or enough, or you stack them.

So basically, though it's an interesting idea, this design is very impractical.