I’m ok with the request to add the option for users to pick, but I take issue with the “half of the world” claim.
The USA is in the Sunday start region per the link, and importantly, know many people in this country look at the week as a Monday start. That is regardless of the apparent classification above, or what happens to be printed on calendars used in this country (S-S typical).
I’d wager that many (most?) people look at Monday as the functional start of the week, through Friday as the real week. And I’d bet they see the weekend as a Sat + Sun period (not split as seen in most calendars). That parallels TRs implementation as well as the basic use I see through so many people in TR and elsewhere in my life.
Options are fine, but the claim above seems inaccurate and potentially misleading to me, with respect to functional impact.