Yes, over at Support for IDN · Issue #132 · plesk/letsencrypt-plesk · GitHub a Plesk developer said
I hope we release it in Q2 2017, as support of aliases and subdomains, but maybe a bit later.
(You could do it today in a different kind of hosting environment, but if you're depending on the Plesk built-in support for Let's Encrypt, you'll have to wait for Plesk to add the feature.)