I'm considering the "ignoring it" approach at least for now. I'll monitor it and see how things go. Thanks for all the input!

: I had a similar cracked rib in my qajaq. I took the approach of
: ignoring it, which seemed to work fine. It did start to abrade
: the skin, but not seriously. A few years later I took the skin
: off and cut the rib out, amongst some other small design
: changes. I'm almost ready to re-skin.

: If you can cut the rib out without too much hassle, go for it.