Agreed on generally limiting the use of bow-ties, but I think you are overlooking the best use-case for them, which is the ability to selectively allow U-turns in different directions at a given intersection. In your part of the country, are there few locations where U-turns are only legal in one, two, or three out of four directions? We have that sort of arrangement at every other intersection in LA, it seems, and they are often in areas where the only alternative to a U is a very long and ugly detour. I don't like bow-ties any more than anyone else does, but until we have junction boxes, they serve a purpose, and not exclusively that of disallowing U-turns.
My own dislike for bow-ties is what led me, in my earlier editing days, to make much heavier use of at-grade connectors for left turns. They can effectively allow or disallow U-turns, but don't fit every situation. I still use them occasionally, but have had so many of mine deleted by the CM clutter police, I resort more often to bow-ties, because they're more likely to stick around.
Well, times do change, and fleshing out the guidance means you'll have something to point to (which CMs should be familiar with anyway). Fortuitously, a few such intersections can be controlled adequately simply by disabling left turns which are disallowed anyway. Others can't, but there are other solutions, like AGCs and box-diagonals, all of which can be configured to give the "turn left then turn left" instruction.
While I do agree with you that "Turn left onto [the road you're on]" is potentially confusing, I don't see how "Turn left onto [something], and then turn left onto [the road you're on]" is really much less confusing. They are both bad prompts, and swinging a U hardly resembles a two-turn maneuver than it does a single turn. Yes, it's nice to hear the name that will be on the sign where you'll be making the initial turn, but that doesn't always happen. Because of issues like street name changes at intersections, we often leave the cross segments un-named. In those cases, the double prompt names the street you're on twice.
But in any of these bow-tie or regular-split intersection cases, a quick look down at the screen will show you a highlighted route with a clear turn-around point ahead. It's an understandable visual cue.
Maybe "turn left then turn left" is a "bad prompt", but at least it's accurate. "Turn left" is just plain wrong. We have to recall that not every user is always looking at the screen while using Waze – some don't have dash mounts, resorting to cupholders, and so forth. If "turn left then turn left" is odd, then at the least it might prompt the user to take a look at the phone to try and figure out what it's telling them to do.
And actually, the double prompt no longer names the street you're on twice in those situations. With the TTS changes in 3.8, it will now say "Turn left then turn left on Street-youre-on Blvd".
I'm not sure how you can say that a bow-tie prompt is "utterly confusing", but in the next breath more or less dismiss the far more baffling (lack of) instructions for an un-split road U-turn. I don't think you are considering just how confusing that can be, and how frustrating it is when it happens at a time and place where a mistake and recalculation can cost all the time savings for which you were using Waze in the first place.
Because you, as an editor, never need to choose between the two. Either the road is unsplit and your choices are "don't allow U turns" or "no instruction at all", or the road is split and your choices are "turn left" (bowtie) or "turn left then turn left" (two lefts make a U...).