I'm sorry but I don't think we're getting F-Zero anytime soon. I think we'll get Diddy Kong Racing 2 this year, then F-Zero MAYBE within the next couple of years. But I do not expect to see anything F-Zero related at all for at least a year, but more likely two at the earliest.
GS4 I think will likely be announced at E3. The main reason I can see it announced sooner is so it can be announced in a Direct before Camelot's 20th anniversary. Then again, they might just announce GS4 on Camelot's anniversary instead. Who knows, really?
Holy crap I just realized, if GS4 comes out next year, its the 15th anniversary of the franchise. How did I not catch that?
Fitting, it could get announced the year of Camelot's 20th, the released on the franchise's 15th.