and I think it will take over twenty years to go to where machines are starting to really displace most of the workforce.

I am not so sure about that. I think it might happen a bit faster. But even if it does take twenty years and you are retired, does that make you safe? The world will be a very different place if 50% of people are unemployed and hungry. So will retirement funds, investments and rent returns.

And I think physical professions such as plumbers will be one of the first displaced by robotics.

Maybe at some point. But I suspect that it might not be worth making a toilet fixing robot who climbs behind cisterns in old houses for a while. But as said, the designs will change.