[Angostura]

Sounds like an opportunity for someone to get control of more than 50% of mining capacity.

[mannykannot]

At which point, could you unilaterally hard-fork it, e.g. to fix this problem with the difficulty-adjusting rules?

Though if that is an option, I would guess it would be more likely for a coalition of miners to choose to do so before any individual achieves 50%.