The announcement sounded to me like they're refocusing Server.app for Profile Manager / MDM than one-application-do-it-all approach like they did previously. I think this benefit even more for enterprise users, because they're likely not going to use the bundled Apache/Dovecot/etc. that came with Server.app, but rather using existing infrastructure they already had in place anyway.

Edit: one thing to note: macOS Server is not an entire OS, but rather a Server.app application running on top of existing macOS installation that you can download from Mac App Store.