At this time I cannot see the Raspberry Pi much good for anything. Especially for providing professional digital signage. However, it does have enough power to do it, it just does not have a correct OS for it yet. I have seen a whole lot smaller processors with less memory in my life that has done much better than a Rpi. (Of course they were not supporting hd video either). So is development improves in the OS so will the Rpi. It is a still a development board at this stage.
I disagree. Since the industry standard in the digital signage-world tend to be images and h264 encoded videos, both of which the Raspberry Pi handles well. Hence, I think the Raspberry Pi is a perfect fit.
My guess is that the Raspberry Pi is capable of running full-blown HTML5. The "only" thing needed is a custom browser that offloads the rendering to the GPU (which most likely is what the players you are referring to are doing). If given proper funding (or time), I'm sure there is someone at this forum that can/will write a Webkit-based browser capable of this.
Also, last time I checked, not even Chrome/Chromium or Firefox on Linux (x86) uses the GPU for accelerating web content. Hence, the Raspberry Pi isn't unique in this regard.
I know that the Rpi is a universal computer, but I also think that it most capable of doing only one thing at a time. It is just is capable is any other computer, but why try to make it a universal machine when trying to accomplish one thing. I would not expect to control a robot with it, and write a webpage on it at the same time, and neither would I put that into the OS to do that.
That is a very naive assumption. What exactly does 'It is just is capable is any other computer' even mean? Not all computers are created equal. You can't compare an ARM-powered computer with your desktop machine. No, not even for single-threaded operations.
Again, I think this is a bad idea, but sure you can do whatever you want. Unless you write a customized browser that uses the GPU for acceleration, you can forget about doing anything fancy like HTML5 on the Raspberry Pi.
Second, forget about Flash. It's a crappy and proprietary format and the modern world is moving away from it (and moving to HTML5 and h264-videos). Moreover, I'd be very surprised if Adobe ever released a version that caters to the Raspberry Pi. Yes, it does support ARM, but in order for it to be usable, it would need to utilize the GPU.
Also if all you want to do is to point your browser to a website, you can hack Screenly to perform this action. All you need to do is to disable some functions. The source code is available, so feel free to go crazy with it.
We are creating Screenly based on our experience and our need (i.e. to power our digital signage network). Since we try to keep things generic, hopefully other people will benefit from it too (and that seems to be the case, judging from the feedback we've received).