It's worth reviewing the reasons that manufacturers got away from solid-tub designs:
* Measuring the water level is difficult. Most solid-tubs used timed fill, which causes a variety of problems.
* Spinning a tub full of water puts more of a strain in the motor and the mechanism. There weren't that many large-capacity solid tub machines; most of them had smaller capacities than users are accustomed to today.
* There's the sock-over-the-side problem. Not that perforated tubs are totally immune from this, but it was more of a problem with solid tubs.
* Solid tubs weren't very good at getting rid of insoluable sediments that settle to the bottom of the tub during wash. We all know about the sediment-ejector tubes that always got clogged up.
In addition, there are modern features that I think would be harder to implement on a solid-tub machine, such as automatic load measuring and water heating.
Having said all that, modern technology could probably overcome all of these problems. For instance, optical load measuring and water level sensing, possibly using a sensor built into the cabinet rim. Lots of modern machines have the top of the inner tub sealed to the outer tub; a tub drain could be incorporated into that such that it would be impossible for an item of any size to escape into the outer tub. Large stepper motors, a la the GE Harmony, have gobs of torque and could spin a large tub full of water with no problem, without a clutch. The sediment problem could potentially be solved by magnetically operated sediment drain valves in the bottom of the tub, using modern high-power magnets; that would not require a physical connection between the tub and the stationary mechanism.
It does seem like a solid-tub machine could be a water saver if it was implemented properly with modern technology. Old solid-tub machines often didn't save water because they couldn't control their fill levels. (And because they did overflow rinses...) Obviously, if you don't have to fill the space between the inner and outer tubs, that should save some water, especially with today's large-capacity tubs.