CellData with a data size different for each CellType.

In the example below, the cell data size is the same for each cell.

 <CellData HigherOrderDegrees="HigherOrderDegrees">
        <DataArray type="Float64" Name="HigherOrderDegrees" NumberOfComponents="3" format="ascii" RangeMin="1" RangeMax="2">
          2 2 1 2 2 1
          2 2 1 2 2 1
          2 2 1
        </DataArray>
      </CellData>

Would it be possible to define a size specific for each cell or each cell type via an offset?

Like the connectivity, the size of the element node ids is specific to each cell type, and since the size is not uniform, an offset table is used. Can we do the same with CellData?

I fear it is not possible - and no filter/rendering technique in VTK can exploite such a feature. So you might then want to use the largest array width and fill unused values with NaN for example.
HTH,
J.