1. Is just a nomenclature problem. The key issue was whether Pluto belongs in the same category as Mercury through Neptune.
2. If a planet changes its orbit, one of two things will happen:
In both of these cases the new category that object will fall in is quite clear
3. and 4. In geological terms yes, but I think the IAU was correct in preferring to define planets through orbital characteristics over geological ones.
5. The neighborhood of a planet cannot be simply changed without significant consequences. If through some freak incident a formerly solitary planet ends up suddenly having a neighbor of significantly higher mass, that planet will not remain a planet for very long. Its "mutability" is then not even restricted to definition games, it will quite be literally destroyed or thrown away into deep space.
6. An Earth-copy that hasn't cleared its neighborhood yet won't be an Earth-copy due to frequent crust destroying meteorite impacts. Such a child solar system will probably not be described well by our current terminology but these systems are also very rare because that phase of life only lasts for a very short time.
7. There will clearly eventually be edge cases, but Pluto isn't. There is an object with 10000 times its mass within its perihel and apohel. Its orbital period is not independantly "chosen" but defined by Neptune
8. - 10. Those are all things that we are just now starting to discover. They might eventually change up the definition of the word planet again, such as when we do find the first binary pair of planets with similar mass in the same orbit. But for now it should be perfectly acceptable to delay that decision until we have solid data.
11+ are mostly political points where you can have an opinion either way. But scientifically the question is: Are Pluto, Ceres, Eris and the 100+ other yet to be discovered KBOs really similar enough to the big eight to be in the same category.
Hokkaido is a bit of a bad example though since there's no Shinkansen service through the tunnel.
Going 1500km the other way to Kagoshima the train takes about 7 hours, and the airplane 5-6 (from city center to city center). That's with the 270km/h regular Shinkansen. If you increased the speed to maglev levels the train would outperform an airplane.
Computer programmers do it byte by byte.