To me am evolutionary dead end would have to be something that not only didn't make it to the present generation of bikes but also either:
Hasn't been accepted by most frame or parts manufacturers despite being around for a while or,
Was used widely at the time but only for a brief period.
So in summary, an idea that only saw one or two iterations. This way things like quill stems, lugs, and canti brakes won't count. Each of these saw wide use in the marketplace.
Case in point would be that Cannondale SE. Flex stem, rigid aluminum fork, and force 40 brakes were never really accepted or improved.
In that case, where all the Activators? Not aware of any other manufacturer using lead for the frame tubes!
If you can't be a good example, be a horrible warning!
Current rides:1994 Orange P7 (project), 1995 Clockwork (the f-in-law's), 1996 Orange C16R (the wife's), 2007 Ltd Edition Clockwork, 2011 Orange 5 Pro, 2014 Planet X Carbon road bike
Previous rides:1993 Orange Clockwork XC Pro, 1993 Orange Clockwork XC expert, 1994 Kona Kilauea, 1995 Kona Cindercone, 1995 Orange E3, 1996 Orange P7 XT, 1997 Saracen Maxtrax, 2009 Orange Evo 8