If I am not mistaken, I believe that this 'new' LTA rule is actually an old rule, which for some reason was made obsolete. The mininum mileage in the past was to ensure that the drivers will keep on the road. But how the new rule is going to impact on the other stated objective of calling for a taxi instead of standing on the kerbside.
I know of an semi-retired insurance fella who ditched his personal car and got a taxi which he uses for sending his grandchildren to school, return to fetch his working family members to the office before coming back to send his wife to her mahjong sessions. And before the repeats the reverse-cycle later in the day, he drops in to visit clients and sending them if the latter need to go somewhere.
There was a report a little while back that about 20% of the taxis are actually idle at the operators'. An update of the figure would be interesting.