This is nothing like DPC. Although maybe potentially concerning in it's own right, but for different reasons.
GraphicStock.com is owned by the same people running VideoBlocks, and it's a similar deal. You don't upload images, you just sell your entire portfolio to them. You keep the right to sell your work elsewhere, but they have a perpetual license to sell your work without any additional payment to you.
Buyers can subscribe for $49/month for unlimited downloads.
I don't really see it as a threat, though. Not now anyway. They don't have many photos, almost none with models as far as I can tell. It's almost entirely graphics and conceptual/illustrative images. I still think most buyers want variety, they want to be able to get photos, illustrations, and graphics all in one place. Especially in a subscription model.
It seems like it could be appealing to buyers, but ultimately it probably won't ever eat into existing companies because it's too specialized for volume purchasing.
The deals I've heard about aren't too bad for artists. For the right price, I'd sell my portfolio to them. Sure you're competing with yourself when you sell to them, but only on the work in your portfolio up to the point of the sale. And only if GraphicStock ever gets bigger. Which I suspect may never happen, and even if it does, the portfolio I'd sell them today will look very different in a few years.
And is it really competition if not very many people are buying images there? Judging by twitter comments it seems like most of the interest in the site is from people who just want to use the free trial and not actually buy anything. No big loss for the competition there.