For example if one wanted to fly to Hokkaido for a week, etc. between trips instead of "commuting home" would immigration allow the pilot to enter on Passport (US/ 90 day visa exempt), instead of a shorepass?
Yes, you can use your passport to enter Japan after your last trip before your days off and then use the length of the tourist visa to visit places. Many people who use ZED tickets will use their passport after their last trip because they may not get on with the standby ticket and then it's a real pain getting a new shore pass sorted out. Only snag with passport is the Japanese putting a sticker in your book and taking up half the page, so make sure you've got lots of spare pages.
Any chance of hiring FOs on the 787 in a few years? (I should have the type)
Well, eventually they will because they'll get rid of all the 767s but this is going to take quite some time. The latest information we had from the Company was there would be no direct entry onto the 787 for the foreseeable future. Your guess is as good as any as to how long that would be. Being type rated would almost certainly go in your favour for the interview but it won't make much difference to the course. Assuming you're lucky enough to have another type rated pilot to pair up with in the sim, then you'd be exempt one of the checks and a bit of ground school but that's about it.