There have been two such breaks, not one. Perls 1-5 correspond to the first such break. Perl 6 corresponds to the second.
If "regular expressions" is taken to refer to formal language theory regular expressions -- which is NOT what 99% of devs mean by the terms regex or regular expressions -- then "breaks with the tradition" (formal language theory "tradition") happened somewhere in the 1960s to 1980s timeframe, when capturing parens and backreferences were introduced in [qs]?ed or similar. (Years before the first Perl arrived in 1987 to popularize and extend said break with tradition.)
If "traditional regexp" is instead taken to refer to this latter notion of "regular expression", i.e to match what 99% of devs DO mean by the terms regex or regular expression -- Perl 5 compatible regexes, PCRE, etc. -- then Perl 6 represents a second break with tradition, breaking away from the currently still popular Perl 5 "tradition".
In other words:
* "Regex" meaning 1: formal regular expressions (from 1950s)
* "Regex" meaning 2: Perl (5) compatible regexps (from 1960s)
* "Regex" meaning 3: Perl 6 rules[1] (first officially available 2015)
If "regular expressions" is taken to refer to formal language theory regular expressions -- which is NOT what 99% of devs mean by the terms regex or regular expressions -- then "breaks with the tradition" (formal language theory "tradition") happened somewhere in the 1960s to 1980s timeframe, when capturing parens and backreferences were introduced in [qs]?ed or similar. (Years before the first Perl arrived in 1987 to popularize and extend said break with tradition.)
If "traditional regexp" is instead taken to refer to this latter notion of "regular expression", i.e to match what 99% of devs DO mean by the terms regex or regular expression -- Perl 5 compatible regexes, PCRE, etc. -- then Perl 6 represents a second break with tradition, breaking away from the currently still popular Perl 5 "tradition".
In other words:
* "Regex" meaning 1: formal regular expressions (from 1950s)
* "Regex" meaning 2: Perl (5) compatible regexps (from 1960s)
* "Regex" meaning 3: Perl 6 rules[1] (first officially available 2015)
[1] "Perl 6 rules are the regular expression, string matching and general-purpose parsing facility of Perl 6 ..." (https://en.wikipedia.org/wiki/Perl_6_rules)