There are definitely no legal implications. There are terms and conditions set out for the Mog Bonanza (and the game) that are clear as day. One of the terms and conditions (paraphrasing) is that Square Enix reserve the right to modify the online play experience with absolutely no notice. That umbrella statement includes the prizes for Mog Bonanza.
Additionally, it's not classed as gambling. This is a common law I have a LOT of experience with first hand. The whole Mog Bonanza is classed as "a game of skill", and I'll tell you why:
Square Enix sneakily implemented this change that I'm very familiar with a couple of years ago. You know how the Moogles inconspicuously ask you now: "You do know why we're here, right?" (Or is the question, "You know what we're selling, right?" -- I forget, not played for a long time -- but there is an initial question before you can proceed to buy tickets).
Either way, that question makes the whole process count as "a game of skill". If you get the question wrong - you can't buy tickets; but if you talk to the moogle and answer correctly - then you can buy tickets.
At which point - the whole process of getting a ticket with numbers on becomes entry to a randomly drawn prize pool (which is only offered after getting the initial dialog question correct).
Hence, it's no longer a lottery. You get the question right (skill), then you're entered into a prize pool.
Like seriously, do you think you're going to scare Square Enix into changing something (that they might or might not have stated incorrectly or accidentally) by weighing in that you believe there are legal implications, and someone might choose to sue? This forum never ceases to amaze me.