I dont think Ripsaw is in need of replacing, or be it Submission.
If Ripsaw was replaced, I'd prefer for it to just be upgraded to a newer, bigger model (not floorless though, I find them less thrilling facing backwards).
As for Submission, as it is a one of a kind I'd rather see it relocated somewhere else on park maybe given a new lease of life, although not everyones cup of tea, its fairly popular with guests and im sure it would be even more of a hit if it wasn't tucked away in a corner with only one side operationg at a time!
Finally, for altons next white knuckle ride, I suggest either a Gyro Swing either located by Sonic, X-Sector or Forbidden Valley(Very popular with the public!).
Or a Fabbri Pandemonium type ride
Clicky.
I am aware there are also rotating models of this ride which look truly spectactular, and would also rival Drayton Mannor's model! Personally, I also think this would fit PERFECTLY in Katanga Canyon if space could be made possibly the coach park or even just on decked platform somwhere over the dinghy resevoir, with the right theming I think it could finish the area off perfectly!