I guess that there will always be progress, look at a 50's 4/4, a 60's 4/4 and so on. The question is where next.
Why have so many 4/4s been sold? Various reasons I am sure. Why did I buy an older one? Not least so I could "tinker". I guess my skills would not allow as much tinkering with a new engined model. I guess I am not alone with this.
That said many owners would not want to tinker and like the history etc.
I guess evolution will and should happen, but I think modern "upgrades" should be options.
One thought: are they so bad they need (note need not choose) these significant changes to the trads? I think not...
