On one of my machines, two of the characters you proposed aren't displayed correctly, because there's no font installed that contains them.

As a maintainer of code like that I would be unhappy to be faced with characters that I don't know how to produce with the keyboard.

In my humble opinion, the real problem with regex readability is that people tend to not reuse regexes, so everything is pieced together from the primitives.

I find

use Regexp::Common qw /URI/;
if ($string =~/$RE{URI}{HTTP}/) {
    ...
}
[download]

more readable than any of the alternatives you have offered, and there are no "weird" characters involved.