I'm not sure how we got from fractionals vs. decimals all the way to completely switching systems of measurement. I'm also one of those folks who grew up with both and it clearly did not *reduce* the number of things I gotta know. In addition to knowing that 1/16=.0625, I have to know that 2.54cm= 1 inch. That's more difficult, not less. There is a saying that says "that's the great thing about standards....there's so many to choose from". We didn't get a replacement standard when we here in the US tried to adopt the metric system, we got *another* standard.
The trouble is that "Embracing" the metric system will inherently be a switching of horses mid stream. We have lots of stuff like machine tools, indicators, etc that would all have to be replaced and that is no small matter.
I guess I also don't understand your statement about single point threading (is there really any other kind for most of us?) on an imperial lathe. Many of us have imperial lathes. We do single point threading. If we "embraced" the metric system, we would need to be cutting metric threads on that imperial lathe....which was exactly the point.
Heading back to the original topic, however, the use of standard fractionals is not so terribly difficult. If a decimal equivalent chart (I have them on about every wall in my shop) is not your bag, learn the standard values for the lowest fractional increments and then you just need to add and multiply.
ie. 1/8= .125, 1/16= .0625 etc. From those you can know that 9/16=.5+.0625 or .5625 without the aid of a table. After working with them a bit, all the common stuff will be in your head anyway.