I fully agree with Innovation and the others calling for LDAP integration to be in the OpenSource variant.
LDAP is not a tool that is used exclusively in huge organisations. I've even used it in small non-commercial groups of people create OpenSource software just because there is so many Logins nowaways. Jenkins, Artifactory, Gerrit, Redmine, Seafile, ... If you want to automate some of the building process it is just a way of keeping your sanity to use LDAP. It is not a feature for "enterprises with hundreds or thousands of individuals that move in and out of teams on a daily basis to make progress towards shared goals".
I was in the process of setting up an experimental Mattermost Server but upon reading that LDAP is going to be an Enterprise Feature I immediately stopped. While the pricing does not seem final yet, you seem to target it for organizations with hundreds or thousands of people and looking at similar pricing schemes for other software, it will probably be far beyond affordable for us. So unfortunately, this is a very big deal and a total blocker. Almost all other projects we use (see above) have moved at least basic LDAP support in their OpenSource editions. If you want to be a real alternative for small teams, please re-consider your decision. LDAP is not an enterprise feature. Even Admins for Teams of 10 like to have all accounts in one place instead of going through 10 different places everytime a user joins.
We are not using GitLab and therefore, using Gitlab SSO is not an option for me. Setting up and managing a Gitlab Server we won't ever use just so we can use LDAP with Mattermost is just too much of a hassle.