In short, I don't think a for-profit attack is likely.
Why, if the ROI of such an attack is positive ?
Government attacks are where the risk is imo, damaging stuff is a lot more viable when you are using other peoples money. We have some advantages though, government is slow to act and difficulty is growing exponentially at least for now.
If the ROI of an attack is positive now, it will be positive at any given time, since minting is not involved in such an attack scenario. Instead, given the FRN/BTC ratio is growing exponentially, the likelihood of such an attack would grow exponentially with time.