Nope. So far, the glyphosate “train” has resulted mainly in rapidly elevating usage of glyphosates; the pests simply become resistant over time, as as both plant and animal pests always have, I’ll note, to ANY poison. Over time, you end up needing astronomical amounts of the stuff, simply to “break even”. Even worse, it turns out weeds even trade genes between different species at times — much like bacteria are known to — thus spreading resistance even faster.
We haven’t come across your hypothetical weed, yet; in fact exactly the opposite, so it’s not a wonderful justification for that vicious cycle. Plus glyphosates very likely causes cancer (although that’s not certain) -.-’ . Even if not, it ends up being a net negative to a farmer’s bottom line.
Additionally, the technology and infrastructure to manufacture w/e witches’ brew is speced for any given GM’d, poison-resistant resistant crop (the vast majority of GM products) is something you’re assuming will be in place, if this seed bank is ever truly needed. That’s a very bold assumption.
Here’s a reasonably good general overview re: the glyphosate “train” from Harvard’s “Science in the News”: http://sitn.hms.harvard.edu/flash/2015/roundup-ready-crops/
