A320 Captain reported significant Flight Control System anomalies affecting flight safety and possible inflight loss of aircraft control.

Narrative

This is a re-submission of an entry regarding this event; submitted here for increased visibility and likelihood that some action will be taken on this flight safety risk. Sadly; given the nature of this web form; all formatting is lost. This aircraft; Airbus A320; had two return-to-gate events; over two days; due to significant flight control anomalies. My main and overriding concern is that the current Airbus AMM (Aircraft Maintenance Manual) procedures for ELAC (Elevator; Aileron Control) failure and/or Aileron Servo Faults are either incorrect; and/or are easily misunderstood/misapplied; and/or can be easily confused with another related (or actually a different causal) flight control defect. On this flight; this likely combination of failures created an extremely significant flight safety hazard (Loss of primary flight controls; ailerons; Alternate Law) just prior to takeoff. In our case; after our first return-to-gate; and after many hours of diagnosis; our over 20-year old Airbus successfully passed all ground tests for Aileron Servo faults; and an ELAC #2 failure; with a 'box swap' with ELAC #1. Maintenance later directed (that evening or early the next morning) ZZZ Contract Maintenance personnel to also placard ELAC #1 'INOP' with MEL XX-XXX. The next day we accomplished the 3- or 4-page test protocols as directed by MEL XX-XXX; which were all passed nominally. Given its significance; we made a specific reference to the note regarding 'After first engine start; the F/CTL ALTN LAW alert may be spuriously displayed. It normally disappears after second engine start.' on MEL Page XXX of X;XXX; (Item XX-XX-XX.X). We had no spurious indications; after either engine start. Furthermore; the post-second engine start flight control check was 100% nominal. However; during taxi; and only 2- or 3-minutes prior to takeoff; and also approximately ten-minutes post-second engine start; we had a surprising Master Caution; triple-chime; with an ECAM page seemingly full of F/CTL error messages; beginning with 'L Aileron Fault' and 'R Aileron Fault;' and 'Alternate Law (Prot Lim).' Along with above ECAM indications; we also noted that both ailerons were 'XX'd' out on the lower ECAM display; and all four aileron actuators had amber brackets around them. We accomplished another flight control check to visually inspect our aileron positions. We were quite surprised to see that both were immobile/locked despite repeated; full; left/right side stick movements by either pilot. (Spoiler panels did appear to extend; at least partially; so we had that going for us.) Called Maintenance to advise of our system failures; they concurred that another return-to-gate was warranted.This event had a massive impact on flight safety; potentially resulting in loss of aircraft control at; or soon after takeoff. A slightly closer gate (shorter taxi time) would have likely resulted in a high-speed RTO (Rejected Takeoff); or with our aircraft at low altitude/low energy; with inoperative ailerons. (Note that there are no crosswind limits associated with this MEL.) Another area worthy of investigation: how/why this aircraft's internal diagnostic software presented such a lengthy delay in alerting the crew to the pending failure of both ailerons. Immediate advisory to Airbus; FAA; and others; regarding this MEL which does NOT require any wait time prior to takeoff to allow all internal diagnostic testing to complete. Anecdotal information suggests that older Airbus aircraft have 'old' ELAC software and that 'new' ELAC software may have prevented this event from ever occurring. If so; suggest an FAA Airworthiness Directive to require new software to be installed ASAP; with a set date in the near future. Suggest significant; crosswind limits be placed on this MEL so as to preclude an aircraft hull loss due to loss of ailerons during takeoff. To reduce risk to the flying public; consider 'Ferry Only' limitation for this and other Flight Control MEL items.