Statistics channel is currently expected to be open only on http port. But it requires setting special Selinux boolean for it.

When port 80 or 8008 would be sufficient, boolean toggle would help:

$ (sudo) setsebool -P named_tcp_bind_http_port=on

statistics-channels {
  inet 127.0.0.1 port 8008 allow { 127.0.0.1; };
};

List of booleans related to bind is described on named_selinux(8) manual page when selinux-policy-doc package is installed.
$ (sudo) yum install selinux-policy-doc
$ man 8 named_selinux

When any custom port is desired, selinux policy has to be modified. First install semanage helper.

$ (sudo) yum install policycoreutils-python-utils

Then add custom port to dns_port_t type, which would allow bind to listen on that port. In this case, setsebool is not necessary.

$ (sudo) semanage port -a -t dns_port_t -p tcp 8053

All current port assigned to a type could be obtained by command

$ semanage port -l | grep dns_port_t

All ports available when named_tcp_bind_http_port=on is set could be obtained by command

$ semanage port -l | grep dns_port_t

Would do you think this is sufficient for listening on custom ports?

I think this is sufficient. Perhaps any sample config files could include a statistics-channel definition with recommended ports that have pre-aligend SELinux policies.  

The Prometheus exporter for BIND uses 8053 in their example 
https://github.com/prometheus-community/bind_exporter 

I'll post a comment there with a link to this BZ to cover the SELinux config

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