I hope Apple is noting the number of complaints about this keyboard design. I think they should make clear in their specifications that it is significantly different from previous models!
The Edinburgh Genius bar failed to fix my keyboard on my second visit, despite saying they would and keeping my computer for a week; but when I threatened to return it for a full refund, they finally agreed to replace the keyboard, necessitating a third visit 48 hours later. Apparently, they have to replace the entire 'top' of the computer plus battery. I read somewhere that Apple redesigned the keyboard in 2017, but the store was unable to confirm this. Anyway, the replacement did fix the problem of stuck keys and double keystrokes and I can now type normally. You just have to be persistent!
I also do not believe the stories that the problem is caused by 'dust'. My first keyboard was a problem as soon as it came out of the box, brand new, and I have done nothing to make it dirty. On the other hand I have had several MacBooks Air before, typically for 4-5 years each with nothing but superficial cleaning, and never experienced such keyboard problems.