Coming fresh from Wikipedia, so my knowledge is... limited at the very best, but I'll touch on a couple of things about the fencing saber that make it less than ideal at best.
First off, the construction of a saber requires it to be thin and flexible, which is fine for fencing, but wouldn't be allowed per the weapon construction rules; your weapon can't bend too much, because the risks of it snapping, splintering, and injuring someone are much higher. The required padding can only mitigate this so much while being squishy enough to be considered safe for combat.
Second, from what I understand, it's designed as a thrusting weapon; thrusting weapons are totally a thing (spears), but the construction requirements for a thrusting weapon include a 2" collapsible thrusting tip that springs back almost immediately (the guideline in our chapter is "fully expanded within 2 seconds"), with non-thrusting weapon foam underneath that. This tends to result in a very boxy-looking tip regardless of any other factors, and I'm not experienced enough in weapon construction to suggest a viable solution to this.
Both of these mean that, at least to the best of my knowledge and skills, a saber-style sword is going to look and feel more or less like a regular sword with a thrust tip on it, and I'm not sure how to mitigate that without compromising the safety of the weapon. (Side note: if you use a carbon-fiber rod as a core, you can make very light weapons, so it's possible to make a weapon that still feels about as light as a saber.)
If you haven't made a lot of weapons before, I'm going to recommend sticking to a more traditional sword style for your first couple, and trying for a more saber-style one after you've got some experience; the guidelines in the 1.3 ARB aren't changing in 2.0, so that's a good place to start if you're brand-new. You should also check in with your home chapter and see if any experienced foam smiths can offer you more help; particularly if you post in a group on Facebook, you might get a speedier reply, or from someone who can show you in person.
Final note, you're probably going to make at least a couple of mistakes on your first attempt at getting a more sword-looking sword, but that's valuable learning experience, so don't get down on yourself even if it comes out looking like it was hacked up by a blind toddler (like mine did). Figure out where you went wrong, and try again.