To be honest, 5 years ago who would have predicted bikes to be getting longer?
I think it would be a very hard job to predict correctly what kind of bikes are going to be popular later on. For example, about 3 years ago, short frames were the nuts for trials, frames such as the zebdi and leesons were both examples of how short frames can makes a great riding trials bike. Then 3 years on, zebdi's are becoming less and less favoured over long frames such as St.Blaise and XTP etc.
But, I don't think that anyone can say that a frame (well, most frames) are going to have a huge effect on your riding ability. Yes, a longer frame such as a coustellier may make you better at backwheeling etc, but it will be detrimental to the manualing ability you had on a zebdi, leeson, curtis etc.
Who knows? Maybe steel copies of the leeson will be next in line for Onza? I'm certainly not complaining if it is. One must also take into account that steel frames also come with a generally high price tag (Leeson, Curtis) so if Onza can produce a frame based around the geometry of the leeson or curtis, but without the price tag, I think they could be onto a winner.