Indeed it has - Douglas Englebart popularized the concept in 1968 with a one-handed layout and device, and several other schemes have been proposed. Prior to ASETNIOP, however, nobody had designed a system that was directly related to the ubiquitous QWERTY layout. Stranger still, nobody had assigned the space bar (the most frequently used key on any keyboard) to a thumb. With the arrival of various new input methods (like touchscreens and gesture recognition systems) and advances in word prediction technology, chorded keysets are now the best possible option for devices that don't have a physical keyboard.
Absolutely not. Learning ASETNIOP is similar to (but much easier than) learning a second language. Actually, it's probably more like an American learning how to speak English with an Australian accent (or vice versa). Once you're proficient, you're no more likely to slip into QWERTY mode in the middle of typing with ASETNIOP than you would be to be in the midst of a conversation in English and suddenly blurt out a word in French. No ASETNIOP users have reported that learning the new system has had any effect whatsoever on their ability to use a traditional keyboard.
It varies. One twitter user reported reaching speeds of 54 wpm after five days of practice. Another user managed a speed of 37 wpm after taking the tutorial and practicing for less than half an hour. Most users won't pick things up quite so quickly, but you can expect to reach about 30 wpm after a couple hours of practice and will steadily improve thereafter, especially once you've memorized the alphabet and don't need to use the visual aids.
Not at all! The production of a letter with ASETNIOP actually takes place upon the release of a key (rather than on the downward stroke), so as long as you press both keys down before releasing either of them, it will register the chord properly. And there's an autocorrect process in place to correct things if you're sloppy and release one key before pressing the second key in a combination, and also if you're too fast and press a second (or third) key before you've released the first.
The primary developer (Zack Dennis) types with ASETNIOP on a tablet at about 65-70 wpm, and has hit bursts of over 100 wpm.
The folks over at Guinness don't have a specific category for this type of method (i.e. virtual keyboards), but ASETNIOP has been used to beat the official records in a number of categories, including "Fastest Typing on a Smartphone," (see video here) and "Fastest Time to Type a Text Message (SMS) on a Touch-Screen Mobile Phone," (see video here).
While you've probably already figured this out, the name ASETNIOP represents the eight primary or "home" keys that can be obtained with a single press-and-release. Many of the features of the system are designed to make it easy to learn, and the name "ASETNIOP" is no exception - once you've learned the name, you've already started learning how to use it.
Swiftkey and Swype are both excellent systems for writing text message on touchscreen phones, but aren't much use outside of that context. They offer no benefits when writing anything that's not already programmed into their native dictionaries - such as computer code, dialogue, vernacular, proper names, places, passwords, etc. Since both Swype and Swiftkey require considerably more motion (both of your hands and your eyes) to use, you'll grow fatigued more quickly when using these systems, which is why they're unsuitable for a desktop environment. But ultimately it boils down to the fact that other methods only use one input point, while ASETNIOP uses ten.
It's similar to the difference between writing with a pen and writing using a typewriter or keyboard. A device that lets you use a simple up-and-down tapping motion requires considerably less movement than a device that requires a lateral sliding motion. Try this: tap one of your index fingers on your desk. Note that only the muscles controlling that one finger need to move. Now try sliding that finger around on the surface in a circular motion - your whole hand, including your wrist (and for some folks, the entire arm) needs to move!.