Well I for would greatly appreciate such a policy. I don't have painful periods, but I do have a very heavy flow. I do a job that depends upon me working outside, often in different unanticipated locations far away from toilets. Depending on which supervisor I have, I either get extra breaks or have to end up asking again and again to use the loo. There have been occasions where even with night time pads, two pairs of knickers etc. I have 'messed up'. I work with the public and often end up standing for long hours which makes it worse. You would think female supervisors would understand, but I find a lot of women take the pill, and have very light, if any, periods and sometimes they just do not get why you need to change every other hour.
For some reasons periods are still a taboo, (despite always ads) and I find some men are great and understand, but a lot are clueless as to why it's important to have extra 'bathroom' time. This despite having mothers, sisters and girlfriends
I have taught both my sons what's involved, (and they hear me complain) as I do not want them growing up finding any discussion about periods distateful.
I do think there should be an awareness campaign, much like there is in terms of women struggling with symtoms of menopause in the workplace.
Some jobs make it less a problem, others, especially those at the lower end where a worker has less 'negotiation' strength, can make it a massive issue by default.
These days I try not to do shifts whilst on my period, full stop as I can't deal with the hassle. This means I earn less.