Anyone here think of using a steelhead rod for crappie? They're longer, like a crappie rod, and most have that mod-fast action, which would be good for the softer mouths on crappie.

Overkill, but they'll work.

Yes and I have thought the opposite too...what if one was to buy a Berkley Crappie series in 10' or 11' and drift fish for steelhead?

Riversider makes a nice and affordable 10' steelhead rod that would be a great panfish rod for like $39.99 at Gander.

By far, the nicest steelhead rod I have seen in person is the St. Croix Wild River 106ML which is rated down to 1/8 and has a great action.  I was able to check it out in Cabela's the other day.  To me, it would be perfect for steelhead in PA and NY and would even serve as a great rod to wade fish for American Shad in the Delaware (which I do with a longer noodle style rod).

I use an old 10' Shimano Convergence with a "Michigan" grip that was meant for crappie with a centerpin reel in some of the narrower ditches that can't accommodate my longer rods.  I believe it was actually designed for crappie fishing.  Worked okay, but you had be careful if the fish was over that 10# mark.

I've even used my medium-mod crankbait rod without issue.  There's no set rules, but there are better tools for the job.