It's just like Windows XP going EOL. A lot of people took their time. Microsoft just stops making updates for it. Doesn't necessarily mean it's going to explode on the day it goes EOL.

My upgrades have been going smoothly so far. It's a very similar process when you upgrade SQL Express to Standard. For the people upgrading from SQL 2012 Standard, you'll need to make your own slipstreamed SQL 2016 Standard installer with Service Pack 3. Then go for the upgrade. There's no SQL 2016 Standard SP3 installer like there is for Express.