I guess maybe I'm not envisioning what you're saying? What I think you're saying is to glue the felt to the magnets, then put the glued-felt magnets on either side of the silk twill to hold it. If so, then the glue will be close enough to the silk to potentially rot or discolor it, even though the glue is on the magnet side, not the silk side. Even fumes or off-gassing can do major damage. It's why I never let my collectors keep their silver in ziploc bags. The plastic off-gasses and seriously discolors (and in some cases disfigures) the metal. Textiles are far more fragile than silver, and silk can be exceptionally susceptible to breakdown.
That being said, I do realize that in this case we're talking about items produced in reasonably decent quantities that don't cost the earth. With that in mind, as long as the buyer knows the risks she's taking in framing, this isn't something that requires the same level of care as a 16th c. sampler, say.
Good to know about the Ikea frame. Thanks!