ARM isn't new.... and ARM processors have already taken off... years ago.
ARM-based processors very much outsell x86-based ones.
Quad-core phones might appear next year. Tegra 3 (4+1 cores) tablets will be out in 1-2 weeks.
You won't see 8GB RAM phones for 5+ years.
1) There are no smartphone applications in the near that need this much memory
2) More RAM means more power draw. If nothing needs it, the RAM would just be wasting power.
My guess is that you might see 8GB of PRAM or Memistor-based RAM... but not SDRAM.
Except there are no ARM cores at 3GHz+.
...and it is not an exact comparision since you have to define "powerful". I don't believe ARM processors do too much (if any) path prediction.
X86 kills arm in throughput, because arm is very stripped down low power design. to make arm as powerful as x86, would pretty much kill the whole low power ideology behind the design.
For many tasks though and a good gpgpu strategy I could see ARM making some inroads in very specifically tasked devices. I think x86 will fix power consumption and battery technology will improve long before arm gets powerful enough to compete in the x86 space.