I just re-watched a show called 'megstructures' where they featured a rollercoster called kingda ka that reached over 200kph in 3.5 seconds and is also the tallest in the world. 

If we put cost aside, and only focus on a) human ability to withstand ride and b) the ability of the physical structure to withstand.  could we potentially see roller costers the height of buildings going at yet unseen speeds and heights?

i understand how some trained people can withstand g forces like fighter pilots.  But keep in mind rides need to be for general public.