Since Plesk Onyx you will be able to install memcache as a Docker container and configure http(s) proxy rule for it to map to your web app.
Docker and proxy rules are available in Plesk Onyx Preview already, you can try it here https://talk.plesk.com/threads/plesk-onyx-preview-and-feedback.337172/
SEMate supported this idea ·Mate commented
Please, do not tell us to use Varnish or NGinx...
Please just provide memcached as a php settting for 7.0, 7.2 and 7.2, this is all we need !