Guys, you're making a big thing out of nothing.
The stable branch will continue to receive normal revisions, the same as Servers always have (think Server 2008 > Server2008R2 > Server 2012 > Server 2012R2 > Server 2016) and the semi-annual channel will receive new builds and feature updates to keep up with technology and software advances/changes, as the "normal" Windows 10 channel is doing now (think Redstone 1, Redstone 2, Anniversary Update, Creators Update, etc.)
Twice a year updates can only happen if you specifically sign up for that branch of development, it doesn't happen by default or accident. Twice a year also means they will be more stable than the "fast ring" of Windows 10 and never like daily or weekly builds.
And if you have to sign up, well then you accept that chance of instability compared to the normal release (LTSB) of Server 2016.
You can also switch back and forth between types of updates, if you choose.
The "regular" updates of the stable branch of Server 2016 will continue to be as they are now, up to the administrator as to when or if.
And restarts will continue to be as they are now, when the admin decides they should be. They don't happen at random, unless you've failed to properly set up your server.