Finally a keyboard for emacs users! But yeah, this is a nice demo. I managed to type 'www.facebook.com' in around 30 seconds. I would be curious to see if it can approach faster typing speeds after some learning and familiarisation. My gut feeling is that it won't because having to take all your fingers off the keys between letters. It might be faster if a chord is registered after a group of keys have been pressed but before they have been released. Still, an interesting idea.
You are right; the way it works now has a low speed limit. Even when in ~70% the cases you can switch hands and don't need to wait releasing all your fingers. When using your suggestion, the implementation has a hard time figuring out, if you wanted to press AS, or press A and then AS. Keyboard inputs are sequential and not simultaneous. But I'm playing around with some timers right now; if a press comes in you have a time window of some milliseconds before the chord is registered. This has a nice effect on bi- and trigrams; in English you often have to type "th". Making this a roll from your index to middle finger, things should speed up. So e.g. J would become 't' and K 'h', then you can press J, wait some milliseconds and press K.