As I have mentioned before, I am not going for any world record myself. If I was though, this is the way I would go about it.
First, I would make sure I had the best 4x4x4 available on the market. I have no idea what that would be, though I hear good things about the V cubes.
Regarding corners:
Whichever system works the fastest is the way to go. I would consider any method used by the top 10 2x2x2 solvers. If the system I end up using is one in use by one of the top 5 2x2x2 solvers, then I would be confident in sticking with it. If my system is not in use by the top 10, then I would have to strongly consider switching, no matter how much I was in love with my system. That's why I gave up Guimond.
Regarding the l and r edges:
I still think that the system which requires the fewest total moves is the best choice.
Regarding the centers, I think that the method I propose may be worth exploring, mainly because of the sheer brute force potential here. Brute force has worked very well for 2 look Last Layer solves on the 3x3x3.
If you were to use setup moves, you would need a whole lot of algorithms for the first center, but still a finite number.
Assuming that you are trying to solve the entire U center in one algorithm, and L and R centers are solved:
3 center cubies solved-
single center cubie on adjacent face
single center on opposite face
2 adjacent solved-
single on adjacent, single on opposite
single on adjacent, single on other adjacent
2 adjacent cubies on adjacent face
2 adjacent cubies on opposite face
2 diagonal cubies on adjacent face
2 diagonal cubies on opposite face
2 diagonal solved-
single on adjacent, single on opposite
single on adjacent, single on other adjacent
2 adjacent cubies on adjacent face
2 adjacent cubies on opposite face
2 diagonal cubies on adjacent face
2 diagonal cubies on opposite face
1 center cubie solved-
3 on adjacent face
3 on opposite face
2 adjacent on adjacent face, one on opposite face
2 adjacent on adjacent face, one on other adjacent face
2 adjacent on opposite face, one on adjacent face
2 diagonal on adjacent face, one on opposite face
2 diagonal on adjacent face, one on other adjacent face
2 diagonal on opposite face, one on adjacent face
one center cubie on each of the other 3 faces
0 center cubies solved
All 4 on adjacent face
All 4 on opposite face
2 adjacent on adjacent face, 2 on opposite face
2 adjacent on one adjacent face, 2 adjacent on the other adjacent face
2 diagonal on one adjacent face, 2 diagonal on opposite face
2 diagonal on one adjacent face, 2 diagonal on other adjacent face
2 adjacent on adjacent face, 2 diagonal on opposite face
2 adjacent on adjacent face, 2 diagonal on other adjacent face
2 diagonal on adjacent face, 2 adjacent on opposite face
3 on adjacent, 1 on opposite
3 on adjacent, 1 on other adjacent
3 on opposite, 1 on adjacent
2 adjacent on adjacent face, one on each remaining face
2 adjacent on opposite face, one on each remaining face
2 diagonal on adjacent face, one on each remaining face
2 diagonal on opposite face, one on each remaining face
39 algorithms, if I haven't missed any cases, and am counting correctly. We already use several of them. The only thing I would ensure while finding all the algorithms is that the opposite centers don't get disturbed during a direct center solve (so that you can use a subset of the 39 algorithms to solve the opposite face centers without messing up the first solved center).
Before giving up on this idea, consider how many algorithms an F2L solver must learn to do a 2 look last layer, or even the number of algorithms that you use for your l and r edges.
If you were to disregard center control while finishing the cage, and knew these 39 algorithms cold, you could save brain space on the l and r edge portion of the solve, and concentrate on crushing the centers in 3 algorithms.
That being said, I don't see how the best 39 algorithms can be found without a search program, so this proposed method will likely exist as a theoretical method only. I certainly don't have the time or patience to find them manually.