I highly doubt the cards are going to be region locked.
The amiibo cards work by reading the data from the card, and finding it in game, unlocking that content. So each card has a certain unique chip number (not each individual card, but each card itself - ie; all Isabelle cards would have the same chip number). So let's say Isabelle's chip number is #ABC001, Tom Nook's is #ABC002, K.K. Slider is #ABC003, and so on all the way up to #ABC400 to account for the 400 amiibo cards they're going to release - and since the Villager amiibo is confirmed to work, his chip number can be #ABC401.
So now that we have 401 different chip numbers for all amiibo, when we go to scan them in the game, the reader will read that chip number (ie; #ABC253) and search the games content for that number, to give you that villager in game. If the amiibo were region locked, then Nintendo would have to reprogram the game for every region to give every single amiibo in that region a different chip number (ie; Isabelle's number in Japan would be #ABC001, but in North America it would be #XYZ999), which is literally so much extra work just for unlocking data in game. Nintendo would essentially need to reprogram the amiibo data in each regions game, instead of copying and pasting it.
Not only that, but it would get incredibly confusing for Nintendo to have every regions amiibo use a different chip number instead of a universal one - they may make their next batch of amiibo figures region-free and spend a lot more time trying to find a spare chip number in each region to hold that amiibo data.
Code digging had also revealed that Nintendo have actually saved certain numbers to be used for potential Pokemon amiibo, so they can all share the same similar values (
http://www.nintendolife.com/news/20...or_a_future_of_pokemon_cards_and_mii_fighters). If they're doing this for Pokemon, I see no reason for them to do it for AC either.
If these cards actually stored a considerable amount of data (which they don't, they only store items), then I could see them getting a region lock. But since no amiibo so far have been region locked, and these are only for unlocking purposes, I don't see any reason for a region lock to exist.
Plus, considering the smash amiibo aren't region locked, that means that any villager amiibo will work in any game, and it'd be kinda dumb for 1/401 of the games compatible amiibo not to be region locked.
The NFC reader makes sense to me region locked, because it's actual hardware, so the programming is different. The amiibo cards aren't hardware, and are a simply chip with a respective number attached to them, and considering they literally just unlock content (and store items for trade - which brings up another point, you trade items through the cards. Trading would be more difficult if the cards were region locked), there's no reason for them to be region locked
