PR #24443 deprecated memcache in favor of memcached. Memcached extension is not available for Windows. So essentially memcached server session mechanism will be unusable on any windows servers.

The reasoning given for PR was that pecl repository does not have a memcache version compatible with php 7, however there is a popular repository which has made it compatible: https://github.com/websupport-sk/pecl-memcache

Our whole infrastructure around 60 servers are all dependent on that session mechanism and we compile memcache extension from source mentioned above without issues (for php 7.0 - 7.2).
If this deprecation is not reverted we, (and any other windows platform that relies on memcache for sessions) will be forced to maintain our own copy of MemcacheSessionHandler which won't be marked as deprecated.