Why would a twin-blade be more useful than an Alaskan sawmill, or a beam machine? If you had a two-blade saw you'd still need a guide anyway...
It's about speed, convenience and a bit about cost. It's just an idea that vertical board cutting would save me some time.
I've worked a lot with chainsaws over the years and here would be some of my concerns.
1. Chainsaws are fiddling machines. Having to keep two chains sharp, tensioned correctly, two chain oiling ports free of sawdust, keeping things cool enough it doesn't bind, etc. would be twice as much work as a single bar. All these will shave away at any speed you gain by using two bars.
2. You need a bigger engine, more fuel, more oil to run two bars so while speeding up your cuts, you are increasing your input costs so I'm not sure there would be a cost savings.
3. How about the spacing between the bars? The video above has the spacing quite far apart, most likely for ease of working on each chain individually. If you were to put them closer together, it would make the chains much harder to work on but you would end up with perhaps something closer to board size.
4. If you've run a chainsaw all day, you always want the lightest chainsaw to get the job done. Even those will feel like lead weights well before the end of a day. Now you double the size of the engine, gas tank and oil tank just to run similar times as a single bar chainsaw and you have a really heavy chainsaw.
5. If you are interested in making boards, their are hundreds of chainsaw mills out there that you can clamp just about any chainsaw in that will saw straight boards at a pretty fast pace.
6. Every pinch a single blade in a tree? It requires a mall and a wedge to get your chainsaw free again. I'm not sure how one would free a double bar chainsaw that is pinched in a tree.