The only issue is lack of 'fun'. Most fish aren't going to be able to fight you very hard if you're using an 8 weight, to the point that you can skip them back to you. Guess at the same point it makes you a hell of a lot quicker at catch and release. Definitely not an obstacle persay.. Also harder on the arms for long days, and aren't going to present dries half as delicately or accurately at close range...
with that, if you're local, and are only going to go steelheading once or twice a year, you'll probably be pretty sick of your 8 in short order on trout..