You’ve phrased this feature request as a means of addressing “registration of bots or other fake people”. We’ve noted that CAPTCHA (specifically reCAPTCHA) is an existing tool in the product which helps with that.
In parallel threads, @asmecher notes that this feature could be considered for 3.x:
and I note the path toward implementing this in 2.x:
You are correct that the value of sorting by registration date is probably more useful than the value of sorting users by email, but given the focus on 3.x, this is an unlikely candidate for enhancement in 2.x by PKP. It would always be a welcome pull request from the community.