Gavra,
What do you wonder?
Also, trousers are untzniusdik for a different reason (the same reason. women don’t ride normally on animals).
First point first:
I wonder how “Makpid” people were at the times of the Rishonim regarding Tznius (especially of non-Jews). It seems that the whole “separate sidewalks” and “please enter our community with long sleeves” is not supported by Halacha.
Second point:
Trousers (L’cheorah, but I am not a Lamdan) would not prevent a man from reading Kriyas Shema (unless you have proof otherwise), as no Ervah is “uncovered”. I assume you have proof to the contrary, but I remember seeing and posting B’shem Rav Vosner that women are allowed to wear snowpants. Of course there is a chiluk, but it is certainly not clear-cut.