I think you are going to have a hard time pinning down the definition of a "traditional" kilt. Most everyone will agree that a kilt that has features A through K (or whatever) is a traditional kilt.

But what if a particular kilt only has features A through J. Is is still considered traditional?

How about a kilt that only has A through I, or H, or G?

Where people draw the line is going to vary so that not everyone will agree.

For example, for a lot of people, a traditional kilt has to be tartan. But, as Matt has pointed out, solid colored kilts can be just as traditional.

For some, only the 8-9 yard, knife-pleated kilt is the only truly traditional kilt. But again, the box-pleated style has an even longer pedigree.

There is not really a definite bold line between traditional and non-traditional, but rather a hazy grey area.