You could, of course, use 4 LED and arrange them to form a bridge rectifier, although I think flicker would still be an issue. Just seems strange that a simple commutator in the hub would remove the need for a rectifying circuit, especially as the capacitor would require DC as well.
That is a splendid bit of pedantry but is it true? I would have assumed it would be a DC output so you could run a standard LED lamp.