WorldLux my understanding is that that is the way it will happen for many aircraft. But this is the first aircraft to be retrofitted and no one knows exactly how long it will take. There must be a very steep learning curve for those doing the job. We must expect that the first aircraft retrofitted will take much longer than when it becomes almost routine.

Add to this delays in retrofitting would take up much needed workspace in the hangers and could cause delay to other, scheduled, maintenance tasks.
Another question is manpower! Is there sufficient manpower to do both jobs at the same time? Would the retrofitting actually interfere with the other tasks? etc.
And many other questions which cannot be answered until there is some experience in the task!
Perhaps we on this forum should hold back from criticising until there are some concrete facts to work with!