I think Petrus would have real potential, if people focused on it, instead of Fridrich. It has fewer moves, but keeping up a good tps is hard. If you practise hard enough, finding the pieces become second nature. If everyone practised Petrus, I think sub 10 averages would be achieved, then sub 9. Beyond that? Sub 8 a12? You need a different method than Fridrich, and probably Petrus. However, I think Petrus has real potential that hasn't been reached, I'm just not a block builder.
Sub-8 avg12? Congratulations, you made me laugh.
Personally I think Petrus does not have quite as much potential (on average) as Fridrich - the block building part does save a few moves, but recognition is harder than for F2L and the moves are a bit less fingertricky. And if you just want to use as few moves as possible, why choose Petrus and not Heise? I'm sure with a sub-40 move average a fast turner could easily break 10 seconds... that is, if 4 tps is even possible with Heise ;-)
IMO, if there's any method out there today (not counting things requiring memorization of several hundred algs) that has the potential to beat Fridrich, it's Roux, but getting fast will still require a ton of practice and some natural talent (as well as being good with M-slices, which not everyone is). But I won't be surprised if in 20 years the top solvers are still using CFOP.