From my experience, glider wings cannot be made strong enough to not flex. So don't have that as a goal.

Also, if you're building an existing design, or even your own original but it uses the same construction method and components from an existing design, I wouldn't worry too much about trying for a major increase in strength.

There are a lot of construction ideas that sound great, but wind up having an application flaw. For example..... the thread. You're hoping for it to provide a significant increase in spanwise strength and rigidity. If you think about it's diameter a minute, it might not seem so magic. If it does provide rigidity, any at all, it's going to have to "distribute" it. So what's it going to be glued to that can buffer that increase in rigidity to the rest of the wing? There aren't too many things that can take what is basically a zero size point that has huge rigidity and not simply be sliced and diced by that tiny "stress riser". What you're basically asking the support structure to do is to stand all that force in what? .05" of it's own area? What materials have that strength?

So you have a root rib out of say aluminum and a tip rib the same. What does the rigid thread do to hold the wing inbetween from flexing? So you plug in some more aluminum ribs. See where this is going.

Surrounding structure has to be matched to whatever stiffens or supports it. I think a spanwise stiffener for a glider wing would have to be somewhat wider and not so rigid. A tape of glasscloth along the spar has been adequate for years. If you don't have a spar, then a wider tape between the foam and skin has worked for years.