Paul Eggert <eggert@cs.ucla.edu> schrieb am Mon Feb 23 2015 at 20:55:54:

Would it be possible to fix the regular expression engine, so that
programs don't have to worry about parsing and reformulating regexps so
that they're "nice"?

See http://swtch.com/~rsc/regexp/regexp1.html for a nice introduction into RE engines. It might be worthwhile to investigate the performance characteristics of using such a Thompson NFA in Emacs for regexes without back references.