Can anyone who either is living in Japan or has visited the offline Japanese Apple Stores confirm that Macbooks (Air/Pro) are sold with either JP or US keyboards? Apparently the online store allows such a customization.
I can't confirm 100%, but I suspect so, considering the demand that they must have for that (I spent a fair amount of time in Japan). Hopefully someone else can chime in and confirm.
I work in one, and we have both US and JP models in stock. Unless there's a new update on the way, you should always be able to get yourself a US keyboard version, especially because customers here prefer JP ones.
Not apparently--you can select US or JP keyboard on the Japanese online store (and the US keyboard Macs come with English user manuals, as slim as those are these days). It's good to know, though, that you can also get one in person in Japan.
I really appreciate that recently Apple has been offering your choice of US, Japanese, French, or Spanish keyboards/manuals on the US online store; I remember when getting your hands on a Japanese iMac keyboard meant importing one yourself (which I actually did at one point).