Why not simply fill up two regular sized bowls with flake and enjoy each one for 1 hour and 15 minutes each? If only it were simple as filling up a gigantic bowl and smoking it. Packing can be tricky. How do you light it if it is really wide? An ember in the middle is going to leave lots of unsmoked tobacco on the sides. Oh, just light it all? Sure, now you have created a blast oven. Oh, I'll make it really tall to make it last longer. Sure, that will be easy to pack. And have to empty ash frequently. And, and, and. And isn't it possible if not probable that lots of moisture could really accumulate with such a large bowl?
Not to mention one might get a bit bored with a single blend for that long. There's a reason the vast majority of pipes fit within a certain size range. If you're that set on a large pipe, just empty out a dog food can, drill a hole in the side near the bottom and attach a tube of some kind. Fill that puppy (play on words there folks) up and puff away for a 1/2 a day. It works best by the way to empty out the dog food first.