I personally feel that a 6 dexterity trick is inevitable. I also feel that 6 is the physical limit of what we can do. What I have tried to do here is lay out my argument.
Let's start with a little history. Way back in the early 90's Rippin' Rick Reece acquired a new, supper spiffy, state of the art video camera, which was slightly smaller than a new car and weighed about the same (these were the days when video cameras used full sized VHS cassettes). He used it, of course, to record himself shredding, as it turns out just in time to capture a brand new move, which Kenny swore was not clean. Through slow-mo replay they were able to confirm the cleanliness of what we now know as blurriest.
This camera could also play in reverse (a function most VCRs lacked back then) and it was while messing around with this feature that they realized that the reverse of some moves seemed very possible. The reverse of blur, in particular, seemed very interesting and later that night Dimitri Kavouras hit the very first leg beater. Thus atomic was born, even if it would be almost a decade before it really caught on.
You see at their hearts most sets are the reverse of downtime moves that are already well known, and historically those sets have lagged behind their down time counter parts by several years and in some cases decades. So why the big lag?
In the beginning someone just had to come up with the idea. When I started playing there were only really two sets in wide use: pixi and stepping. I can't speak to the history of pixi but stepping itself was an evolution. If you've ever seen "Tricks of the Trade" you may have noticed that the blur Kenny does is actually mid time. But players did figure it out and in retrospect it seems obvious. If you'll remember your Newton you'll realize that however fast the ball comes down at the end it had to come up exactly as fast at the start and if there's time for a downtime dexterity then logically there must be time for an uptime dexterity.*
Although there is enough time for the dexterity the second difficulty with sets is acceleration. To illustrate this lets compare a butterfly to a stepping set. For the butterfly you set the bag, slowly raise your body and your dexing leg and then turn your hip and let your leg fall over the bag, landing with it. For stepping your leg travels over the bag at the exact same speed, however, instead of slowly building up to the dexterity and falling into it, you need all that speed right at the beginning and against gravity. If you don't believe me about the speed watch a video of someone doing ripwalk. If they're doing it correctly it will look almost exactly the same forwards and backwards. Fortunately the dexterity is relatively slow so high sets are not a problem.
If we compare barfly and furry set, the principle is the same, however because the complexity is increased that initial burst of speed at the beginning of furry set becomes more extreme. Remember for barfly you're using your whole leg like a whip and concentrating that speed into the dexterities at the end of the trick. For furry you need all that speed right at the beginning and again against gravity. There's also one more problem. For the down time barfly you can raise your body up before the trick and fall with the bag as you do the dexterities. For the up time furry set you have no such luxury. If you raise your body up with the dexterity you have to wait for gravity to bring you back down again, wasting time between trick elements. So all the dexterities have to be completed with all the speed up front and your center of gravity more or less stationary.
Difficult, but once people figured out the timing furry set too has become common and if the set isn't too high then it's again pretty much a straight rewind. Watch a video of a clean nemesis forward and backwards and it's pretty much a mirror. And indeed since there's time for 2 dexterities on the way up and 2 on the way down it was inevitable that a 4 dex move would be hit and it's become a very long list.
If we look to a 3 dexterity set it becomes somewhat more complicated, there just aren't a lot of 3 dex down time moves: flurry, double over down swirl, mofly... there are more but it's not a long list. However, they do exist and once again, if there's time to do 3 dexterities on the way down, there's time for 3 on the way up.
It this case though it's hard for me to see the exact way forward, because although the time is the same, the way you do the dexterities is not. Because you need all that speed right at the beginning there are just certain leg positions that work and some that won't. Double over down swirl is a pretty common downtime move (often midtime), but it's hard to picture how you'd gererate the momentum for swirling furry. I'll try to avoid speculating too much on speciffic sets, however I will say that several seem quite feasible and some have obviously even been hit already.
So, my argument comes down to this: if there's time for three dexterities downtime, there must be time for 3 dexterities uptime. Historically sets have lagged behind downtime components because the timing is harder and I think that's the case now, we just have to wait for someone to figure it out. If you put the two elements together sooner or later someone will hit a 6 dexterity move. Thanks for reading.
*As someone who has studied physics I realize this is a gross over simplification, but it's close enough to practical reality.
To see Ken Somolinos' rebuttal go here.