I think a second obviously different kind of sensor would have encouraged the pilot(s) a little bit more to think about a ditching.
The Report touches a very important point from my point of view, which is partial or perceived systems knowledge and how it can lead to potentially dangerous alternative solution paths to a given problem taken by the pilots. In this case partial systems knowledge led them to apparently assume that only the pump(s) /sensors failed (where there were indeed 2 of them).
In a hostile environment where alternative A (complete loss of Oil) looks grim (ditching with SS4 floats in >SS4 and cold water), it's easy to be tempted to consider any 'better' alternative B (It's only the pumps or the sensors...) if there is any ambiguity...
The only problem I see with level sensors is that they even fail to work reliably in the comparatively benign environment of automotive engines.
I'm afraid they would cause a disoproportionate amount of false alarms thereby reducing their value to close to zero.