Hello!
On the server side we run OpenVPN 2.5 to offer ChaCha20-Poly1305 on the Data Channel. OpenVPN 2.5 is still in beta testing, although some key functions are performed by OpenSSL or mbedTLS which are stable, so we mark servers running OpenVPN 2.5 as "Experimental" (you will see them listed with the yellow warning color). OpenVPN 2.4.7 does not support ChaCha20 on the Data Channel so it's a no go (note that OpenVPN 3 is a library with client only, and not server, features).
When OpenVPN 2.5 stable version is released, then ALL of our servers will support ChaCha20 on the Data Channel. Estimated release date is November 2019 according to OpenVPN community. In the meantime please feel free to use ChaCha20 on the experimental servers, of course.
We can expand the network of experimental servers if we receive requests. Currently the servers in Canada and the Netherlands seem enough to support the traffic of clients using ChaCha20, but please let us have your feedback!
Kind regards