[dtech]

A second (time) is already defined on cesium transition, a meter (length) is defined as a fraction of the distance light travels in a second. Both things which we can accurately measure for some time now, and which universal and stable over eons.

What is the problem that would be solved by switching to a single element?

[madengr]

I don't recall. I just read some article recently about trying to define time and length with sodium; trying to define everything with a single element that is very common. Of course it could also have been a 50 year old Asimov book.