1. Is it possible to use the index (and not some property inside of the item) as x-coordinate?
If you are in a scatter mode, this is not possible (scatter mode is when you are using two linear axes and scatter series). If you are using a categorical series (and at least one categorical axis) you will achieve the desired effect by only setting the ValueBinding and not setting the CategoryBinding property at all.
2. is it possible to specify a dot-separated path inside the XValueBinding
You can use a GenericDataPointBinding:
ValueSelector = dataItem => dataItem.Smth.Val
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