SSH no longer listens on custom port after update to 10.12.4
I found the answer here and it appears to also apply for upgrading to Sierra from a pre-el capitan version of OS X.

To summarize:

sudo cp /System/Library/LaunchDaemons/ssh.plist /Library/LaunchDaemons/ssh2.plist


Edit /Library/LaunchDaemons/ssh2.plist and change the lines that read:

&lt;key&gt;Label&lt;/key&gt;
&lt;string&gt;com.openssh.sshd&lt;/string&gt;


to:

&lt;key&gt;Label&lt;/key&gt;
&lt;string&gt;com.openssh.sshd2&lt;/string&gt;


And change the lines that read:

&lt;key&gt;SockServiceName&lt;/key&gt;
&lt;string&gt;ssh&lt;/string&gt;


by replacing "ssh" with whatever port you want to use.

Then start the new port with:

sudo launchctl load -w /Library/LaunchDaemons/ssh2.plist


As noted in the article, this doesn't eliminate ssh running on port 22.  In my case that was okay - the main reason for running on the new port was to match the port ssh was visible at outside the firewall.