I assumed this was intentional. With Bounded Accuracy, it's not going to come up often that you have an unpassable saving throw. Having played and run since 5E came out, including 2 campaigns into the epic tier, we've not seen this happen once.
I assume this is also intentional. While much more likely, flat modifiers are just not common enough in 5E to make this much of an issue. I actually built my last character around this idea, so that I couldn't fail a Concentration save against the minimum DC 10. I feel if a character dedicates that many resources towards avoiding a failed save, it shouldn't be punished because of an arbitrary rule.
Seriously though we have kept flanking from the start even though it is an optional rule. We use a sort of bloodied where I place a red circle near the mini when he is about half and on it when it has one hit left. We also somehow play with rogues being able to backstab if they go first in a combat even if the bad guys are not surprised.