Lior: There is nothing inherently immodest about knowing when a woman is a Niddah or not. Bizman HaGemara, everyone knew. You had to to properly be Makpid on Taharos. Nowadays, when the only Nafka Minah is a Tznius issue, so it seems immodest. But if we create Taharos issues again (as you just did) then there should be anything wrong with it.
As I said earlier, though, this really isn’t so relevant as many Achronim have said that we are not Noheg like this Chumra and have already been Doche it.