There is no reason to believe that it wouldn't be possible to overflow the chain value in other modes too. The game has only been out for a couple of weeks so surely the scoring hasn't been fully optimized yet. Incidentally, does anyone know how long did it take for people to counterstop Guwange / Futari?
I'm guessing no one complaining about this is ever going to replicate it. No sooner than they'll counterstop Futari Ultra or Guwange, at least.
This is just silly. Some people have reached it in just a few weeks already, why couldn't we do it given unlimited time?
So far this seems lot more serious, since both Futari and Guwange require near-optimal play for the whole game in order to reach the max score near the end of the game (or in the end game bonus for a full lives clear in Guwange). In this, the earlier stages are now completely pointless since you can presumably only get that high chain value in stage 5. The older games were also based on optimizing the normal scoring extremely well while this is just bug abuse.
E: It also has nothing to do with the hit count, but the value of the chain breaking the upper bound for a signed 32-bit integer which seems to mess the score calculations pretty badly.