Here is how many reachable nodes are on the network supporting these users, along with the original version release dates:
The key question is is a little complicated: how many full nodes do we need for the current users, how many do we need for double the current users; how many do we need for 100m users; and how many do we need for double that again?
Rather than ask those questions first, I thought it would be interesting to get a common base for how many nodes do we need for the current user base of between 2m to 10m going into a growth period which might see numbers go up to 30m?
Lets ignore pruning; segwit, etc. Those are fantastic technological advances, that I would call tricks of the trade to make everyday users lives easier. The backbone of the network is always going to be full nodes.