I am not a big fan of the hexagonal board I, as its shape makes it difficult to use in a standard context.
One of the unique feature of the Xiao is its compactness. So I would prefer III over II. Now, the micro-SD card slot and the battery cell holder could be easily added on the rear side of the board.
On the III proposal, are the Grove connectors vertical or horizontal?
All those new options do not discard the minimalistic initial E option.