Why not? Both airlines already engage in price fixing HND-CTS and other routes without Shinkansen competition, so they might as well make it official./sarc
Seriously, I would hope this does not happen as I believe the competition with JAL to be good for the industry. As much as I love NH, I don't want to see a situation where they totally dominate domestic air travel in Japan. It's probably inappropriate to compare NH to DL in any way, but DL's been playing dirty tricks since the path was cleared for it to become the world's largest airline and I don't care to find out what the "enhancements" of a JL/NH merger would be.
And JANA? Pass.