... and the only reason for it to be four columns is that you personally find it hard to read, or do you have another, more compelling argument against using 8 column tabs?
Personally, I find 8 columns to be an incredible waste of horizontal space. I frequently place editor windows/panes side by side, and using 8 columns or spaces wastes valuable screen real estate.
But this isn't just a reaction rooted in practicality. To me, this looks and feels absurd. It kind of hurts to read. Again, this is just my personal take.
I prefer scope indentation of any kind to render as 4 spaces, but I'm okay with 2 as well.
It has the -tabwidth option, defaulting to 8. I have yet to figure out what it's used for, but presumably there is some case where it is used for alignment.
It was only used when you invoked the other option to use spaces instead of tabs. Both options are now removed. gofmt doesn't care how wide your tabstops are.