Hello Don, 

There seems to be more into this... like

Client Software (MUA – Mail User Agent)
Should pass the domain name to the MTA (Mail Transport Agent) in A-Label format (RFC 5890).

looks mismatch with clients... as

Our test suggests that Outlook 2016 and Mobile Mail Client passes U-Label , not A-Label , Irrespective of SMTP Server is advertising SMTPUTF8 or not. 

This is probably ok, as when outlook is being configured if server do not support SMTPUPF8, user won`t be able to configure outlook at all, and obviously won`t be able to send email. It looks like Outlook assumes that if the EAI account is configured, than configuration host/server supports necessary standards. 

Server Software
Should confirm EAI-readiness (e.g. advertise SMTPUTF8 support) when making connection to another MTA. 

may be replaced with

1) When Server connects to another SMTP Server, receiving server should advertise SMTPUTF8 in Hello/Ehlo response. 

2) When Mail Client connection to SMTP Server, It should advertise SMTPUTF8 in Hello/Ehlo response. 

The sending server need not to advertise any support for SMTPUTF8, however must follow EAI guidelines while sending data to receiving server. 

Now people who wishes to test their servers against EAI support, may use this tool https://eai.xgenplus.com/ to check.

Regards