Get rid of it completely.

Players shall not call a ball "out" unless they can clearly see a space between the line and the ball as it hits the ground.

There is already a rule in place that governs line calls: 6.C. A ball contacting the playing surface completely outside of
the court is out. Seeing a space between the line and the ball as it bounces is impossible from certain angles, even if the ball is out by 6 inches or more.

A singles player would not be able to call an out ball "out" a majority of the time on a long ball on the service line.  I have many pictures illustrating this.  Also, this is a rule that was misinterpreted from tennis, where a mark is often seen, and the rule was devised primarily for tennis clay courts. The rule was something like, "A space must exist between where the ball lands and the line." That's much different than, "See a space between the line and the ball as it bounces." By creating this rule, you've made it illegal to call a ball that is 6 inches or more out, out, depending on where you're standing. Once again, singles players would be forced to play those balls long on the baseline. I also have pictures illustrating this.

In doubles, this creates an even bigger problem if following the existing rules that govern play in other areas.  If in doubles, the receiver's partner calls a long ball at the at the service line, and it was out by, say, 3 inches.  The receiver is back against the fence returning a hard serve, so at that angle, the ball could be out by more than that and the receiver would not be able to see a space between the line and the ball as it bounces, especially if the serve were coming directly at the receiver. So ball well long.  But server (with 20/200 vision, ha!) questions the receiver.  Receiver, by the rule, can't call the ball out, so would have to play it as in. The receiver's partner has the best angle to call the ball, but the receiver himself has to play the ball as in, meaning he can't, by the rule, call it out.  Now, he could confirm that it was out, but he'd be wrong according to the rules, because from his angle he couldn't see a space, although he is absolutely sure the ball was out. He could say that he didn't see it, which would be a lie, since he did see it, but he didn't see a space, so it's determined to be good (if a ball isn't out, it in).  He could also say that he didn't have the best angle (which is true, especially if using this insane rule), so he's leaving it up to his partner.  But again, even though he didn't have the best angle, he still didn't see a space between the ball and the line, nor could he in many situations even though the ball was out by many inches.  Therefore, he is either forced to lie, feign ignorance, or play the ball as in.  Now doubt exists, and the point goes the the opponents on a ball that was many inches out and that both player know is out.  We all know that players sometimes actually don't see the ball and will defer to their partners, but just as one player sees the ball in, and one sees the ball out, that's doubt.  For both partners to see the same ball differently, they both had to "see" it.  It's no different when a players actually "sees" the ball, knows it's out, but doesn't see a space.  Once again, he's forced to lie (I didn't "see" it), or concede the point as doubt again exists.

And the clincher is that players have to follow this rule, but refs don't?! I've questioned the head of the rules committee and the head of the refs, and both have said this was instituted because refs are unbiased and it would keep the cheating to a minimum. This shouldn't be the basis for a rule that must be followed by one group of people and not another. It shouldn't be the rules committee's responsibility or duty to police morality. If people are going to cheat, they're going to cheat. And nobody follows this rule anyway, especially in singles. Our brains are capable of interpolating and processing data without having to see a "space between the line and the ball as it bounces."

Also of note: if this is the logic of this rule in pickleball, imagine how far the ball would need to be out to call it out in some other sports.

6.C Is a perfectly worded and sufficient rule. "A ball contacting the playing surface completely outside of
the court is 'out'."