This move essentially splits Amazon off from the Play ecosystem. I mean they already had their own store which people would "invest" in, but adding a currency/gift cards/freebies will only increase the lockdown/isolation further.

I'll leave it up to the reader to decide if this is a good or bad thing but for me: I am skipping Amazon's ecosystem in the foreseeable future and sticking to a more open alternative (namely the Play store, which works on most Android devices - including Fire tablets).