People have been saying this for 10+ years. No reddit alternative has proven to be viable. So the people at reddit know that "mass migration" is an empty threat. Where will you go instead? That's right. No where. Rather than quickly bleeding out like digg, reddit has simply achieved a stable stagnant equilibrium. It doesn't grow, it doesn't shrink. It just stagnates and rots.

The easiest tell is that nobody in the comments is posting alternatives. I remember during the digg migration, people unhappy with digg would post on digg telling everyone to try reddit.