Of course it is an issue -- otherwise museums would not worry about replacing the matting eventually to deal with atmospheric acidification/pollutants. There is some mat board that actively fights contamination -- buffering and such -- which might need replacing less often..
But granted it is a rather minor issue. And we are talking storage beyond our lifespans here, too.
And I am pretty much 100% with Ralph on the finishing work and display of our prints. I am not just an image-maker, but also a print-maker. It is what I find rewarding.
If you use the proper mount to begin with, it's NOT an issue. That was my point. Museum board or specifically rag will last as long as the print image or longer.