Well one huge problem here is that we, as tax pros, can tell people "have $X withheld and you'll be fine" but that does NOT translate into anything useful for this new W4. An iterative process - fill it out this way, see what the first paycheck looks like, fill out a NEW W4, see what the 2nd paycheck looks like, is both way more than most folks are willing to do and needlessly work-heavy for the PR dept too. There *should* be a way for a taxpayer to say "$X per paycheck" and be done.
My personal feeling is that there should be ZERO withholding, and everyone should just send in quarterly checks. That will make them think *very* carefully about what/who they vote for! Yes, it's hard for some folks (less so under the TCJA). That's part of being a grownup. But it also would get the employers OUT of the tax business and back IN to the business of running a business and dealing with other employee concerns (where they should be active).