In the case of Japan going for Alaska (instead of BC) then it needs to capture it on J2 so that the air units can land there on J3. This leave the US a chance for attacking (since SZ 1 & 2 are adjacent). If the US bought an additional transport on US1, then on US2 it lands 2 inf., 1 art. and 1 tank (+ 4 fighters and 1 tact.) on Alaska and has 40% chance of winning (Here I include bombardment which wouldn’t work if Japan had split its fleet between SZ1 and SZ2; the US might even loose the sea battle to 1/2 the Japanese fleet). In the game I played, the US won with a tank and a fighter remaining.
J3: Japan is now forced to land transported units (using 6 trns bought in J2) on BC. US responds with all out attack on US3 (7 inf., 1 mech., 3 art. 1 tank, 3 ftrs) with 97% success and builds 60 IPCs worth of units in WUS.
Thus with the new fix (i.e. the one-time 30 bonus IPCs for an early Japan attack on the US), the US has good odds (though not perfect) of defeating this direct attack. I’m sure smarter US players than myself with think of ways of raising the odds on Alaska, but I think the KUSAF option is a viable one for some Japanese players depending on the US player’s purchases. In my opinion, having viable, though risky opening move makes the game fun! This might be like the 4-move checkmate in chess: a rare opportunity to win quickly if presented by a player making the wrong moves.
Thanks for the update Krieghund and for vonLettowVorbeck1914 for posting this play!