In general Blizzard never says anything is allowed - they only ever say what is not allowed. And when they do that they don't even provide enough detail for us to figure out what exactly that means.

As for why some of us spend huge amounts of money for stuff that doesn't work, or may not work in the future - its simply because we want to.

I know several people have started to think of multiboxing almost like a job - they need to farm enough to earn tokens for all their alts. They actually play to make money at this game. I guess that makes sense to some people, and I'm not here to judge what people do with their free time. But if you're looking at hardware multiboxing through that lens - you are correct. This does not make financial sense. You will likely never make back the money spent on the hardware you use to multibox. Most of us playing with all the new ways to multibox within Blizz's new rules are doing it because we like to tinker with new hardware & software. We like figuring out what is possible and what isn't - even if that means we have to spend a lot more money on our hobby. If you're not one of those people, then don't do it - wait for others to figure it out the hard way.