The return section would have to end up being dry to keep the water from turning stagnant plus that would be wasted space in the tank. I would stick to one corner or consider moving to the center. My son is setting up a 40 breeder reef right now with a drain and 2 return lines placed in the center pointing to the outside edges.
why, the return doesn't have to be anything more than a pipe coming up from the bottom. Absolutely no need for a "compartment" for the return if that is what you are thinking.
He really only needs pipes, siphon and return, overflows are not crucially essential
.
I would do it exactly as the OP intends, drain on one side, return on the opposite, and that is actually the proper way to set-up any type of filter system. You want to circulate the water from one area of the tank to the other, and from the bottom to the top.
Placing the drain and return on opposite side guarantees that more than if return/drain originated from the same area of the tank, even with directional return flow.
Just because something is commonly done doesn't necessarily mean it is the best way to do it.
There's something to what Adam said above. Other than just added water what would be your real benefit? (unless you plan to make BOTH a display tank)
Well for one thing you can greatly increase the biological filtering capacity of the system, thereby allowing for more dense stocking and much, much more leeway and latitude concerning water quality and overall stability.
The biggest caveat to a sump set-up is increased evaporation.
I always set-up my tanks so that the biological filtration has the potential to support a population many times what I intend and I have never had any issues with parameter spikes or "mini-cycles".