You can play other 3DS games via wifi-connection regardless of their origin because these 3DS games are no-culture games.
You can play for example Mario Kart 7 with no cross-continental barrier because it has no country-specific culture. Mario Kart 7 JP, EU and NA have exactly the SAME features therefore cross-continental town visiting is possible. Furthermore MK7 was released in the SAME WEEK in JP, EU and NA, it was meant to be played globally.
AC: NL however totally differs from other games. It has culture, different holidays, traditions, it IS country-specific. Also the late release dates are evidence that the gameplay will be changed and new features added and others left out. It will be DIFFERENT and therefore cross-continental town-visting will not be able. Nintendo didn't want to disappoint players so they didn't say it won't be impossibe. Also it is exaggerated to say that Nintendo wants to connect AC players with different cultures. I'm sure players in Hiroshima and Nagasaki are not keen on ever visiting an American town.