“stifling amount of missing features. It’s basically bare-bones SQL server”
Yes, SQL Server missing a ton of functionality: SQL Express. Not quite ready for prime time. But perhaps if there is a lot of interest they’ll improve it.
That's probably what will happen, assuming interest appears.
Microsoft is shifting all their product offerings to "subscriptions", meaning they can screw with the product continually forever and you pay for it all along the way.
Consider Windows 10, which is also "not quite ready for prime time" in a number of critical respects. The underlying OS is fine, but there are so many things missing in the UI that it's incredibly frustrating at times.
I suspect the SQL offering for Linux will be like that. A slow evolution toward what it should have been at release.
But this is only a preview. I'll cut them slack for that. :-)