As with the extractelement patterns that are currently in vector-combine, there are going to be several possible variations on this theme. This should be the clearest, simplest example.
Scalarization is the right direction for target-independent canonicalization, and InstCombine has some of those folds already, but it doesn't do this. I proposed a similar transform in D50992. Here in vector-combine, we can check the cost model to be sure it's profitable, so there should be less risk.