Is this different than with bitcoin?
To short bitcoin you need an investment that exceeds 50% of mining hardware cost.
To short RaiBlocks you need a 50% entire market cap investment.
Yes, it's different. See this discussion:
https://bitcointalk.org/index.php?topic=1382241.0This is relevant, because Raiblocks uses the PoS security model.
Since putting a block in an accounts's chain requires it to be signed by the account owner, how does the stake key holder sign blocks for an account it doesn't have the key for?