It would be handy during long deco stops.
I've learned to use packet drinks with a straw, or just water bottles. I've also seen some guys use a camel back style apparatus but all require removing the mouthpiece to drink.
I have a SCUDA.. It changed my life!. It can be hooked up to an IV bag. No need for any valves, you have to sqeeze the bag to get water in the regulator. I used to get Kidney Stones from 10+ hours of breathing air.You win the Kewpie doll.
It's a Self Contained Underwater Drinking Apparatus.
Starts at 1:27
Have not had one since I started using the SCUDA.. Too bad they are not made anymore. Ill rig a modified mouthpeice with a plastic insert for the water hose.