Sure, that's why I mentioned the Therminator. It has in and out ports on the same side and may very well go 'back and forth' for all I know. This would pretty much double the surface area, I'd think. (and the price..)
But other than that, the main homebrew suppliers plates (Duda, Shirron, Braztek, etc.) are all basically the same construction it seems to me and just vary on total surface area. Not that I've owned them...
I believe the therminator does have the fluid pass through the top part of the heat exchanger, make a turn and then come back out on the original side it goes in. We can actually have these made, but i don't like how there will be added pressure loss to the fluids, and in the case of beer brewing, you have clogging issues for sure. This pressure loss though will reduce your cold fluid flow within the heat exchanger, thus reducing the amount of cooling power of the unit. the point of more plates is to reduce this pressure loss, not so much give more heat transfer.
There is also more to heat transfer than just surface area. Flow of the fluid has a great play in the heat exchange. While surface area allows for more conduction to occur between the fluids, faster flow actually brings many times more heat transfer through convection. Turbulence of the fluid also increases heat transfer tremendously, which is why the channels are corrugated. The faster you send that fluid flowing, the more heat transfer you will have. This is why a longer unit does better than a unit with more plates. You are able to achieve faster velocities and the fluid stays in the heat exchanger for longer time. With more plates, flow is actually reduced as the fluid fills all of the plates and although it exits within the same time, there is less heat transfer occurring.
I would not say the therminator gets more surface area by its design either. If it is making 2 passes, it's practically the same as passing through a heat exchanger twice as long and with half as many plates. it uses half the plates of the unit for one pass, the other plates for the other pass, and covers twice the distance of the heat exchanger. Actually, the fluid doesn't even use all of the beginning and ends of the heat exchanger anyway, I would see some loss coming in on the ends for the bending and going back as well as the ins/outs. Although this is probably negligible.
In the heat, it seems that a longer heat exchanger would be better than the therminator's design simply because of the pressure loss issue. Flow is reduced with that unit and this is especially bad for the cooling fluid as you need that to move as quickly as possible to remove all of the heat from your wort. I would imagine they chose this design not for heat transfer, but for convenience of connections.
Hope this helps everyone in the thought process of heat exchangers. many believe more plates is better, but it is not really true for most applications. Freon applications require many more plates for pressure drop reasons, as well as width. In the case of trying to go for the most efficiency, length is the way to go. use plates only to be sure your cooling fluid is not too restricted when passing through the exchanger.