I think it's a very positive thing, but it's not going to be a game-changer overnight, if ever. Don't get me wrong, I like it.
First of all, expect the environmentalists to scream their heads off. It doesn't matter that it's carbon-negative, it allows the continuation of the our current car-culture versus forced mass-transportation and heavy urbanization, and they're very much against that. They do not want people driving cars. Understand that their goals are political; they want to change our culture, not solve our 'energy' problems.
Second, although these crops are not a food staple (such as corn, currently used as both food and for ethanol production) as such, arable land still competes for crops, by which I mean that a farmer is going to grow whatever is most profitable on his land. If it's corn, then corn. If it's Miscanthus giganteus, then that's what he'll grow. I would expect food prices to soar or gas based on Miscanthus giganteus to remain scarce and pricey, but I would not expect low corn and low biofuel prices. There is only so much arable land, and much of it is in use now.
I hope the research continues and I hope that we see progress in this area. However, I'm not over the moon about it; one will note that E-85 has not become a game-changer, and it was touted in the same way. All the new ethanol production plants? They're bankrupt now, just like the big electrical companies like Solyndra. This could end up being pretty much the same thing; but you never know, and we have to keep looking, that's for sure.