PayJoin adoption

PayJoin is a privacy improvement for bitcoin. In the case where a customer pays a merchant, they both together co-operate to create a single bitcoin transaction which mixes both their coins and masks the payment amount.

Transaction surveillance companies heavily depend on the common input ownership assumption which is broken by PayJoin transactions. So if those transactions became even a little bit widespread they could massively decrease the reliability of blockchain surveillance. Merchants and customers who adopt PayJoin would find their privacy improved from anyone analyzing the blockchain, for example a surveillance company spy would find it much harder to figure out which addresses and transactions belonged to a particular merchant that was using PayJoin, or who else transacted to them.

PayJoin transactions are indistinguishable from regular bitcoin transactions by design, so it's very hard to get an accurate number for how common they are.

The PayJoin protocol standard most likely to get adoption is BIP 0078.

Like any new feature, PayJoin requires a little bit of time to first set up. But if your business suffers from being spied on (for example you're a p2p exchange or bitcoin casino, and regulated exchanges keep banning your customers) then that cost is well worth it.