When I was first coming up in astrology oh so many years ago, there was a book called Arachne Rising, proposing a 13th sign. Now, the discussion is about Ophiuchus. Now, Ophiuchus is technically on the ecliptic. But I think what we may need to realize is that this is not a new phenomenon.
What is different now is that some very slick anti-astrology skepticism is picking up on this as an argument against astrology, as you can see through sites like: http://www.griffithobs.org/SkyOphiuchus.html. On the one hand, this website is completely correct. But that same page actually mentions part of why this issue is being raised now, and it has nothing to do with astrology. In the 20th century, it was the astronomers who redrew all the constellational boundaries so that all of the sky is defined. In other words, you have a fundamental re-definition of what a constellation is. The traditional idea was that a constellation like Cancer or Virgo was a recognizable group of stars that looked like something, and therefore meant something. Constellations were seen as being discrete: in other words, there was "space" around them. When astronomy seriously separated from astrology in the late 17th century, it maintained the old definition of constellation, while stripping it of astrological meaning.
Then, astronomy, in going its separate way, engaged in massive study of the sky with vastly superior telescopes. The more they looked, the more objects they found: more stars, and ultimately, galaxies, nebulae, clusters, etc. Under the telescope, the sky ceased to look like a series of discrete pictures, and by the 20th c., astronomers had realized that the constellations themselves were not "connected" in any way: the pictures only look that way from Earth, because the stars of a constellation aren't necessarily "near" each other in three dimensional space.
Thus, astronomy needed a system for ascribing location, and that meant that they needed to cover the entire celestial sphere, not just the ecliptic. Within this quest for locational accuracy, they redefined the constellations as zones of the sky: yet further divorced from the original pictures of our ancestors.
Then, in the ultimate irony, they come back and chide astrologers for not adapting their changed coordinate system, a system that might as well call a location in Leo as A-150X16 as anything else!
So: back to Ophiuchus. Is there any meaning to having the Sun in Ophiuchus? Maybe. The astrologer who I think knows the most about fixed stars right now is Diana K. Rosenberg. Diana for years has talked about the overlays of the tropical, sidereal and fixed stars. She's also talked about the fact that, using the traditional system, any ecliptic degree actually represents an overlap of several constellations. The fixed stars have always been seen as factors that should be considered in the delineation.
As to whether one should change the zodiac, I would be very reluctant to muck with this when the driving force is coming from a group profoundly hostile to astrology. But apart from that, if the ancients knew there were other constellations which intersected the zodiac, why didn't they incorporate them? Largely, we don't know. There's no historical evidence on this. We've got no one to ask. Whether it's because Ophiucus-Serpentarius (it's really a dual constellation) is simply so large, and that only a small portion intersects the ecliptic, who knows? We can certainly can and should modify our delineations for planets in that region based on the constellational overlap. But junk the old system because 20th century astronomers re-invented the wheel? I don’t think so!