The idea of mining is sound, so I can't imagine it'll ever truly become impossible to profit. We'll just be moving to new currencies, or the next valuable distributed farm technology will come up. I find it hard to believe we won't find another use for the massive number of calculations the world can put out at the moment.
golem is another option as well. thats another distributed mining option where you get paid to let others process images and such...if etherium goes proof of stake well have 1000 million dollar corporate nodes instead of individual miners...is it a good or bad thing? who knows...