HND flights, both to/from the US and SE Asia, are timed for local O/D traffic rather than connecting traffic. There are some possible connections off the afternoon US arrivals, e.g., JL to PEK/PVG/TSA and NH to SGN, but as you can see they're quite limited.

The 351s are meant to be one-for-one 77W replacements, so I wouldn't expect anything to change substantially in the medium to long run. JL/OW and NH/*A have been deprioritizing US - Japan - Asia connections for a while now. It's just more noticeable on the JL/OW side since AA's Asian network is so small, whereas UA can still get you to the likes of BKK and SGN through TPE, SIN, or even NRT (they have more NRT flights than AA's lone flight to DFW).