It hits Grounds and Rocks that Raichu doesn't like while letting it use another Hidden Power type instead of Ice or Water (allows Grass or whatever else it could use). And no, it'll probably stay NU because there are many other Electric-types that are still pretty strong.
Surf Raichu is good, but the hard part is actually getting a legit good one. I don't know too much about this subject however. I haven't heard of a Raichu with Extreme Speed before.
If you want to talk more, move it to my profile page.