When Fnatic were playing in the spring split they were noted for heavy early aggression with Yellowstar roaming much quicker and more effectively than other supports, and Huni has always excelled at great use of TP. Deilor and his staff do meticulous research on their opponents and will prepare them well. I wouldn't think they'll be caught off guard by a fast push comp.
I think they'll end up losing to SKT or EDG because in straight up, old fashioned nuts and bolts laning mechanics they'll be outclassed over a best of 5. I expect Faker, PawN and Marin, in particular, will prove to be clearly better than Febiven and Huni, and smart rotations and pick/ban phases can only cover that up for so long, especially with their extreme champion pools and junglers as smart and experienced as Clearlove and bengi (neither of whom gets close to the credit they deserve). Their bot lane will have to do a lot of work, and they definitely have a non-negligible chance of sneaking an upset, but LoL history has shown that it's very hard to beat better solo lane players over 5 games.
I also think they deserve the hype - this is the best western LoL team there's ever been, and in terms of relative strength with Korea and China, likely the best since the days of M5. And not only that, but seven months ago three of the players were unproven rookies! I think it's interesting how many of the great LoL teams have shot from nowhere to the top in (relatively) short spaces of time (consider CJ Blaze, Moscow 5, Najin Sword, TPA, OMG, SKT-T1 K, Cloud9, KT A, new Fnatic). Even the Samsung teams didn't take much longer than a few months to dominate Korea after being finalised.