Of course it will grow. And people will turn off their miners and complain about how they will never make ROI. However consider this: If you had bought an S9, and run it non-stop through the past couple of years through bitcoin crashes and peaks you still would probably have beaten the ROI numbers at 50k a coin.

I have not done the calculations for a Neptune or even a Titan (previous generation technologies) but I'm guessing even those may show a positive ROI over the years. An L3 is pretty recent technology so it might be worth it.