Much more sensible to just use a designed-for-two-engines plane like the 777X as that point, even assuming the A380 even could do it (which it can't). And if 2 engines were the minimum it needed to fly, then it would actually need to use 3 engines, so that it could survive an engine failure. If you only have 2 engines spun up and you needed both of those and 1 goes out, you've lost your redundancy. You might not even be able to get another engine spun up before you hit the ground.