I don't think any of us can predict about 5 or 10 yrs down the road.
However, what we can do, is do our own tests by duplicating the conditions. Eg. same fabric, same treatments, same starching (or not), etc. And to remember that with different variables, what is OK this time, may not be the next time, because something may be different.
The same goes for chalks, and other types of markers. Test! Test! Test!
In addition to some of the comments above ... the Frixion pens have been known to bleach out where they have marked. Often their disappearing act is all that is noticed, because they have been marked on lighter fabrics. If you look close you may see the bleached line is there. I know, I have seen that happen on lighter fabrics ... as well as darker ones.
So, I'm very cautious using the markers on the right side of fabrics.
Love their fine lines for marking on the wrong side where the risks aren't so high.