Thought this might be interesting. Some of the entries thus far may have to be discussed.
As others have pointed out we're after evolutionary dead ends.
My feelings won't be hurt if you remove mine...
I look forward to some actual dialogue....
Drum brakes don't have a place in modern mountainbiking. They were put to rest early with lighter cantilevers, V brakes and eventualy disc brakes. Possibly a good idea on a Toronto winter commuter but not real mountainbiking. If you disagree, I look forward to hearing your rebuttal.
Double top tubes (or some variation of like lets say a first Gen Breezer) were a poor design that added unneeded weight with the onset of higher quality metals.
Saddle suspension. Certainly if you are going to the store in Amsterdam and may drop the occasional curb, but it is dead as far as mountainbiking goes. Am I wrong? Even the suspension seatpost doesn't have a place ... Wonderful examples of obsolete technology.
Coaster brake? Enough said....
Look forward to some articulate rebuttals.
Seek: Cunningham, Koski Trailmaster, Breezer Series II or III, Early Ibis Custom.