I actually suspect that the next tallest and fastest "traditional" coaster we'll see will be like Rossa. Huge, effin' lift hill, colossal drop that nags the height and speed records, then a Ka-like trim hill. Proceed to swish around the layout at ~100 km/h. Huge effin' hills, lifts or not, are extremely expensive, so you'll want to build as few of them as possible. Huge effin' turns and overbanks also cost money, so the cheapest thing to do would be cutting speed before continuing with the layout.
Also, as stated earlier in this topic, I somehow suspect that the next tallest coaster in the world is already built.
Also, as stated earlier in this topic, I somehow suspect that the next tallest coaster in the world is already built.