There's a new attack on blockchain which I'm not sure has really permeated into the community yet in order to really begin to determine if it's really a threat or not, I personally haven't come to fully understand it yet, but it seems plausible.

The way it works is that blocks could be pooled and hashed and added to the chain in groups and because when different additions to the chain are verified the way the contest between competing additions to the chain is resolved is by taking the longer chain, if you could hash more than one block at a time and release several blocks at a time you've automatically got a longer chain and yours will be added to and will be the one to win.

This supposedly would facilitate a 51% attack somehow, that's the part I'm unsure of yet, but there's a mathematician (one who's collaborated with Nassim Taleb in the past so he's no slouch) who claims this could facilitate such an attack.

I'm bullish on BTC, I think it will replace the fiat system ultimately, but I'm not totally sure it's quite perfected yet. Also, I'm not sure how you'd incentivize anyone to run nodes and hash blocks when it comes to a voting system.