Me, I would have done inboard doublers, but that's an aluminum guy talking.
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I understand. These composites have quite different properties from simple metals. I’ve no idea how other configurations would serve in this instance. However, it is clear that this “fix” of routing out the web of the stringer to allow more flex has been investigated before. Certainly adding other structures would have been much more difficult to do in the existing aircraft.
If this doesn’t work, they’ll go back to something that probably requires separating the wing from the body of the aircraft, and what you may suggest may be the result.
I DO believe, though, that this is something that they are kicking themselves for failing to do from the get-go. Something that simply “fell through the cracks.”