I personally prefer no GUI, because it gives me a better impression of security and makes the choice of the host environment far more flexible.
But I see where you're coming from; most people these days prefer mouses over keyboards and if they can operate it using only a mouse, they are usually willing to pay for it a few times more.
On a related topic, I heard Bill Gates once said that, according to their research, if a product had a letter X or V in its name, they could sell it for 20% more

Anyway, this specific feature seems very hard to be made user-friendly and secured at the same time.
I spent a lot of time trying to simplify the process, but I agree that it still isn't something that Gavin's granny could handle.
I will be looking forward though to see how other people approached the problem.
Sorry that I have no time to check it out and test a bit in Armory, but I will gladly watch the video, because from description in OP the process doesn't look much simpler than mine.
In fact it seems quite the same. The only difference I see is that you have a central point that collects the signatures from all the parties, whilst in my case people come to add signatures one after another and the last one to sign can just broadcast the transaction out.