Aside from the fluff, the mechanics are not that good a match.
Here are the pros and cons as I see them:
Pro: Ability score bonuses are great for arcane/divine combination.
Racial ability is similar to elven accuracy.
Cons: Too many languages -- does a shadow elf need anything
beyond Common and Elven by default?
No ability to see in dark (not even low-light vision).
Racial abilities too much focused on light (shadow elves live in the dark).
I think I would agree that the shadar-kai are a better match -- many of
their abilities actually do overlap those of eladrin.