[DennisP]

People are working on things like Truebit and zksnarks for Ethereum, but those still depend on base layer consensus for posting the proofs. They just reduce on-chain computation.

Augur just launched a couple weeks ago.

Preventing validator set manipulation is an important part of sharding research. Part of the solution is getting good random numbers that can't be manipulated, and there are several approaches for that.

Cross-shard communication gets complicated. There are some ideas for it, but that's several years down the road. It'll still be a big step up to have lots of shards, each with the capacity of the full blockchain today, sharing the security of all of them but not getting swamped with traffic if something gets really popular on another shard.