Things would hardly go south unless somebody FUBAR on the ROE and gone trigger happy, just somebody gonna feel the chill due to sanction-tariffs and other punitive measures.
ASEAN got very little collective legitimacy and very incapable by all account, its prima-delta agenda of "not interfere with member states' internal affairs" made it incapable to do anything more than an economic forum (in contrast, EU has far more power, but too much bureaucracy) - just look at how incapable it is to deal with the annual smog comes from Indonesia's slash-and-burn farming practice!
This whole mess is a pretty good example, all it ever takes is one errant shot, and with so many competing parties and interests and so many units to control, its only a matter of time before more incidents like this start becoming more common place. And the role nationalism should never be discounted, Abe is clearly enjoying the spotlight and using political capital to garner support, this could lead to at the very least more visits to Yasukuni and the Koreans i'm sure would never put past the Japanese to use this new found freedom of force to leverage claims on the Dokdo islands.
Other than that, this could be a re-emergence of client/vassal style politics, splitting political alignments according to who backs who, though ideally the US would enter serious negotiations before it balloons to that point, reeling in Japan would be another issue altogether.