Just thinking about it, Steins Gate seems like a tough one to dub. The things I can think of right now are Mayurii's "tuturu", Feyris' "nyan nyan", all the 2chan memes, mispronouncing "hacker", and references to Dr. Pepper (maybe it will be like Code Geass' Pizza Hut and taken out altogether). The Japanese VAs were really good and did an awesome job with things like Okabe's laugh.
This is probably going to be a tough dub, and I'm sure even if Funi does a good job, they're going to arouse some fan-hate.
What worries me most is just Daru's voice in general, I wonder what the heck it's going to sound like in the dub.
I would love Crispin Freeman to dub Okabe.
Dr. Pepper was shown as Dk. Pepper in the series, so it's probably not product placement. I think Funimation could tinker around with the words to make it sound slightly different, but not enough to confuse anyone. Character trademark sayings/laughs could easily be done, it just depends on how good the voice actor is. I've seen some fandubs tackle that problem very nicely.
And even if the dub sucks, just watch the episodes in Japanese audio with subtitles.