Ripple did this several years ago. This was fun, but they stopped it because this giveaway was gamed like hell by guys who had access to HPC clusters. I got a lot of XRP renting AWS compute instances

Did too. This could be easily managed by only making payments to Byteball verified accounts (Jumio), and limiting the payouts to a reasonable amount of computing power. What Tony needs is a lot of people with small rigs, not a few people with huge rigs.
Great idea if it will be fine tuned so as to be reasonably sure than nobody will be able to rig the system - as it often happens when there are givaways. We have recently seen it happening with the Byteball quiz.