The U's give you 'everything' so that might present new issues when trying to quickly switch to U1/U2. Other U settings might not be exactly what you want. The closest I can get to solving this is menu f6, 'release button to use dial'. This makes it a one hand operation when I have my big lens on and need to always support it with my left hand. So with f6 turned ON, I can tap the focus mode button, then move on to the wheel. With a little practice remembering which direction to go, I can do this pretty quickly and switch between area modes. This also works to make the other back buttons like iso a one-handed operation.
In say d9, 21, etc, the point chosen is the starting point. For a bird on the water, I can get away with leaving it in a dynamic mode. However, a bird in the tree confuses focus with my Sigma 150-600 and I must switch to single point. A button would be nice. I have one of my front buttons programmed for spot metering. It would be nice to have the other button jump to single point focus.