I'm not at all sure that LAX-NRT will be dropped. It could be scaled back, it could be plane swapped, or it may stay as is. It depends on how the LAX-HND route does and how the LAX-NRT route does after the LAX-HND is running a while.

I don't see any reason for LAX-NRT to be dropped due to the LAX-HKG route starting. People connect in NRT to way more places than just HKG, and some of them (including intra-Japan flights!) more practical from NRT than from HKG (and more practical from NRT than HND). But, in any case, AA doesn't care that much whether people connect at NRT or if NRT is their final destination, AA cares how well LAX-NRT sells. So it's data-driven (and data-forecast-driven), not dependent on what route they start (with a totally different plane type) to a completely different location in Asia.

AA is announcing it is expanding out of LAX, not just shifting routes around at LAX.