I find this encouraging.
A while back we worshiped at a United Reformed Church of North America Congregation and the pastor would, on occasion, give up his pulpit to an Orthodox Presbyterian minister who lived about an hour away. They have also recently reached out to a PCA congregation and those pastors are trading Sundays on occasion.
One of our PCA pastors has preached at 2 area RPCNA churches and an OPC church on many occasions.
The PCA and OPC met concurrently for a few years, but seem to have drifted apart since then. RPCNA is exclusively acapella Psalms, while there are ARP churches which are as well, and others seem to be trending that way, instruments and hymns are a major barrier for some of the larger congregations.