[snip]

It seems to me that both using a special prefix or adding an option are
adding a lot of baggage and will increase the learning curve.

The nice thing about (3) (even without slicing) is that it seems a v.
natural extension. But (2) seems magical (i.e., Perl-like rather than
Pythonic) which I really don't like.

BTW I just noticed this:

'<_sre.SRE_Pattern object at 0x9ded020>'
>>> "{0!r}".format(rx)
'<_sre.SRE_Pattern object at 0x9ded020>'
>>> "{0!s}".format(rx)
'<_sre.SRE_Pattern object at 0x9ded020>'
>>> "{0!a}".format(rx)

That's fair enough, but maybe for !s the output should be rx.pattern?