Not sure why they went with that octagonal shape. It doesn't look like the skylight itself is octagonal. If it were me, I'd have a contractor re-frame and re-drywall to make it rectangular. If you need an overhead light there, get an electrician to add cable lights with a fixture

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as below:

Definately a unique look. If you truly won't use the fan, replace it with a great chandelier. Not sure what your preferred style is but there are so many to choose. Keep the wood beam in the middle in the wood color.

A simple globe or bowl fixture would work well.