It's not just possible, it's already happening, and happening very fast! Be ready!
It is possible if we scale via off chain solutions. If we focus on scaling via the main chain we will end up centralizing (further) both miners and nodes. The question is where is the limit (e.g. what node count should be considered centralized)? This visualization could be expanded with the Lightning Network added to it (although not sure when we should expect a release).
Node count should be considered centralized when people with decent computers cannot run a node on their bedroom, this is I think very clear. If people can't run a node on a single computer, its when the centralization process starts and once it starts it will expand like mining, it will end up getting "specialized", so it's crucial that we never get past that point where people can run nodes at home.