This shows an evident increase in the adoption of Bitcoin all over the world, although unique addresses does not necessarily translate to unique users of the network, it shows the growth of the network.
Is this evidence of Bitcoin going mainstream?
Would an ATH in addresses lead to a new ATH in the price?
One of the things that people play with is the number of addresses that contain some
BTC, but this does not mean that they are addresses that are specific to the individual user. Every user who is buying/selling, participates in signature campaigns, bounties or any other activity which requires a valid
BTC address probably owns hundreds of addresses.
This is not evidence that
BTC is going mainstream, much less any indicator of new ATH. We have people who think that the number of addresses should be some benchmark for the price (Tom Lee and his stupidity), but it has nothing to do with it.
If you want to know
"when next ATH", just look at Bitcoin history charts.