As you know I was a proponent of NTA providing such infrastructure before we had commercial players. However, NTA won't disrupt a competitive market so that ship has sailed.
Potential disadvantages of a NTA app would include it's inability to exclude drivers who act the bollix - the DAA licensed villains never lose their licences for overcharging, in fact they don't even lose their DAA permits. We have even seen evidence of convicted drug dealers using union support to challenge Garda decisions to refuse their licences.