I've recently got a question I would like to quote and answer.
But "new generation" doesn't really mean anything - what's the old generation? who defines it? - and adding the phrase just confuse the reader, who would expect some description of distinct generations in the article. The distinctive elements of the sports should be described in the article, not hyped with phrases. And any sport that's underwater is inherently 3-dimensional, even if UR makes somewhat more use of the vertical axis than other underwater sports (although not all of them - e.g., underwater football or Aquathlon (underwater wrestling)).
I would say common sense defines the meaning of the phrase. UWR belongs to a group of sports which have been developed in the past decades and are defined by the era they were born in. What I mean by this is that we have inherited a lot of sports from the ancient greeks, like wrestling, which are seen by the western world as the classic/olympic disciplines. And there are also many sports which have different, but still long traditions, like soccer or football/rugby. These are newer generation compared to the first types, they are mostly team sports. And then you can find a group of sports usually not older than 300 years which were called to life by the industrial revolution, like water polo. And then there is the newest generation of sports which are made possible by a 2nd boom of development in wealth and technology as the atomic age started when all sports started to be more affected and later defined by the media and the internet. I believe they are many ways significantly different than the previous sports. UWR and UWH and other smaller teamsports are kind of an exception in this group as it mostly includes extreme sports which are broadcasted to many, but done by few. Many people buy expensive mountain bikes suitable to be ridden off a cliff, but it's rare to see someone riding the same level as the person on the videos who influenced these people. Even less fly wingsuits, ski across avalanches or free solo long trad routes on mountains and so on. Wikipedia on the history of sports goes as far as spectator sports, professionalism and performance-enhancing drugs and only leaves a short note about "post-modern" sports.
New generation might sound like a buzzword, as it is. Post-modern would sound alike, and wouldn't even describe it as well. These are the sports around us which gain popularity quickly as sometimes a well made video goes viral, grants worldwide recognition for the sport, and money is invested in it, but the interest lowers as the element of surprise fades. These sports, being developed in a modern era, show a way different approach in general, a great example could be X-Games. Underwater rugby allows mixed gender teams to compete as well, while large sports are yet to start such debates. Also many of these young sports like UWR have not yet settled into a governing body properly on international level, which is their disadventage, as they are not represented, but on the other hand, it's also an adventage as they are community-driven, like Wikipedia.
And yeah, as noted, not just all underwater, but all sports are inherently 3-dimensional, but very few (extreme dodgeball) take adventage of this vertical axis as UWR. In underwater hockey you are also given the freedom to swim free but the gameplay is still 2 dimensional like in soccer. Trust me, I suck at it, but I still like to play it.
This was the first time I've heard about underwater football, I've looked it up, but to be honest it seems like one of the many local alternatives of UWR.
The concept of UWR in the Wiki article is the most common, "German" understanding of this discipline, just like the way UWH started in the UK and later widespread in the US, Canada, Australia, New-Zealand, this one got popular in Europe, and according to Facebook likes it is accepted as a legit sport by 30.000 people. But I've got to know other people over the net who played it differently and have recognised it as something of their own local development. In Oceania, Japan, etc. surfers train with rocks and call it rock rugby. In Hungary, military divers did something similar to UWR in a shallow pool until they've adapted the common rules from the Czech Republic. I've got messages from freedivers from Asia and Hawaii, who play almost exactly the same game, but in the sea or in the ocean. I believe unless underwater football manages to broadcast their matches, they are going to either adapt or disappear, the same way an early version of underwater rugby had disappeared from the US. I've found a Times magazine from the 40s in which they play a US version of water polo which was more like underwater rugby, and later the country have adapted the more common European volleyball-like concept of polo.
I agree that Aquathlon should be labelled 3D as well.
So that's why I've used "new generation". I wont be able to cite any study on this, as it is so new, only recently have a few sport university studends started their studies focusing on underwater rugby. Please, if you have a phrase better than that, which still describes the above, let me know.