This adoption business feels like a red herring. If one person wants to protect his or her files, one person adopts it. If two people want to communicate, two people can adopt it.
GnuPG is a free and open source implementation of the standard for over 25+ years -- a genie out of the bottle, available on pretty much every platform. There's no shortage of documentation, implementations, or people who will help.
While things like instant messengers and email /can/ integrate it, it's not required to use it. You can encrypt a message and copy & paste it into your messenger or attach it as an email. It's independence is precisely why it's powerful. Anything that wraps its implementation and integrates it into a communications path is inherently a risk / vulnerability in that it can observe or use your private keys on your behalf. That requires more layers of trust.
Maybe it's like the ham radio stuff: We don't need everyone to join, but if we had one person on each block or neighborhood, ...
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