You said that this extension was not implemented anywhere, and you were 
wrong.

I've found that it IS implemented in Perl 6! Look at this discussion:

http://www.perlmonks.org/?node_id=602361

Look at how the matches in quantified capture groups are returned as 
arrayref's (i.e. references to a numbered array).

So my idea is not stupid. Given that Perl rules the world of the Regexp 
language, it will be implemented elsewhere sonner or later, notably in 
PCRE, awk, vi, sed, PHP, .NET library...

Already, this is used in CPAN libraries for Perl v6... (when the X flag 
is set for extensions)