I've always thought the standing martingale thing as a fashion statement was worth an eye roll! I don't really get it and don't use one myself unless I'm afraid the horse I'm on is going to flip his head up and knock out my teeth... But there are many (MANY) who firmly believe that it's part of the look. And I've even been to judges clinics put on by very prestigious judges who have said that it completes the look and "breaks up" the neck or something. I didn't really get it but one did mention that he didn't think that many horses had an attractive enough neck that they could get by without one! strange huh?
As far as it being "illegal"... not as many things are "illegal" as people think they are. But many many things can be penalized at a judge's discretion for being "unconventional". Standing martingales are accepted in over fences classes. All other martingales are not "illegal" but are considered unconventional, which might as well mean illegal.
Where are you guys seeing all these non-D ring bits? They are still huge over here! I'm not in Wellington/HITS right now but all the pics I'm seeing of people are still of them in their D rings! The eq ring? still dominated by pelhams for sure... I don't really get that but that's just me! (feel more old fashioned by the day...)