That there is likely a non-technology reason why online test have not expanded beyond "pilot" capacity of 5k applicants. Recall when the pilot was launched, there were high hopes for rapid expansion. It's a bit naive to assume the slow progress is due to technology scalability. Notice radio silence out of IRCC on their online test plans.
That is making a large assumption. Online testing seems very simple but it is full of potential problems. Speak to anyone who has switched to online teaching this year. The are huge issues with cheating and the lengths to which people go to try to cheat and the lengths schools are having to go to try to combat the cheating are incredible. Nobody has found a good system and schools are having to deal with how many people to fail, put on academic suspension, etc.