I suppose it is logical that The Blade, Ripsaw and Enterprise are nearing the end of their lives, they are some of the oldest, if not the oldest, attractions in the park.
However, they do still draw in decent queues and Enterprise has had quite a bit of money spent on it recently, likewise Ripsaw regularly has a good chunk of money spent on it during the closed season. If they were to be replaced, I wouldn't be surprised if it was a straight swap or a very similar ride.
The problem AT have with flat rides is that a lot of the more modern rides are quite big, they take up a lot of space and are generally quite high. Their current one's all have very small footprints so finding something with decent capacity that they can squeeze into these areas will be quite a challenge.
Anyway, we're deviating from the topic of SW8 so should probably move on from the flat ride situation, there are plenty of topics where that would be suited!