Perhaps it may be more effective to take a different look at the problem. Let's look at why you'd want a weapon that demands fluidity.
Consider what we are trying to maximize. The answer you reference specifies "hard to start moving, hard to stop moving, but stayed fluid whilst moving." Now, if you really think about this, all three of those are really negative traits. Hard to start moving means you can't respond very fast. Hard to stop moving means if you miss, its hard to recover without losing control of your weapon. Staying fluid while moving really says "weapon doesn't respond to every stimulus you could want to give it." That set of criteria is actually quite an undesirable set of weapon characteristics.
So let's look at the heavy weight example: a mace. Let's pick a heavy one, so that we have all of the characteristics desired. It's slow to start, slow to stop, and generally you try to keep it moving to keep control of its inertia. So why would anyone want this? When it comes to heavy weight weapons, the answer is easy: power. If its slow for you to stop, its hard for the opponent to stop it also. Once the mace is in action, the opponent most move out of the way, or take substantial effort to deflect/block it.
But if we want a light weight weapon that is hard for us to stop, what do we get for it? There are many Chinese weapons which are light weight and require absolute fluidity of movement. They all stem from the same goal: the weapons provide control in subtle ways. Consider a Kung Fu Sword. I swing my sword at you, and you block it. If the sword is lightweight, it bends and keeps going a fair distance beyond the block. The sword tip may even point at your face (scary!). If only there was a way to keep striking.
As a matter of fact, there is. Kung Fu does not teach that the strike ends when the block occurs. The block is simply a melding of the two swords for a moment. There is still a pointy bit that is moving towards their face. If you can keep control of that pointy bit, it doesn't matter if they blocked you or not. You can continue to strike.
The trick, of course, is that you need to stay connected wit the tip of your weapon, and that's what the fluidity is for. Even during something as violent as a steel on steel collision, you want to maintain control of you weapon. The Chinese approach to this (and the approach of many Asian arts of war) is that the sword is not treated as its own thing. It is an integrated part of your body. Thus they care as much about the position of your shoulder blades as you swing as they do your wrists, even thought the wrists have such an obvious effect on the direction the blade is pointing. When your opponent blocks, they try to disrupt the movement of your body/sword. If you can refuse to let them disrupt you, your attack moves through their block.
So what does this mean? Look for weapons which give some benefit in exchange for their strict rules. As an excellent example, lets look at the Chinese dart, which is not a melee weapon, but is an interesting test case. The dart's fearsome power is its ability to change directions rapidly. The practitioner is constantly adjusting the length of the dart's chain, and it is often very hard for an opponent to predict exactly how the dart can move because of this.
However, fluidity is essential. If a motion is not fluid, it puts a kink in the chain which flows outward to the dart, disrupting your control. You basically lose control of the dart when you aren't fluid, making it dangerous to absolutely everyone within reach. Unfortunately, while your opponent can step out of reach, you must be in the middle. Failure to be fluid often causes the dart to hurt yourself!
So a near-future nanotech solution? I'm going to redefine rigid to mean it is not exactly pliant to your will. Let's make a nanotech sword which can change shape to wrap around an opponents defenses. However, defensive techniques catch up. People quickly learned a particular defensive pattern which involved getting close enough to the hilt to confuse the nanoparticles (which are not very bright) into thinking their commands were as valid as the original wielder's. At this point, they take the sword over, and kill the owner.
The solution is a ferocious beast: the living sword. It's quiescent state is that of a plain dull grey sword, showing no special properties. However, as the fight begins, it begins to bring its own "mind" into the fight, trying to accomplish whatever it thinks is right. To stop the defensive move that worked against the earlier evolution, the sword does not respond to your will instantaneously. It responds slower, making certain that the only input it really listens to comes from the wielder (because they can hold onto it the longest). If it detects the discord which naturally occurs from two masters trying to control it, it immediately snaps forward back into a dull grey sword and waits for the outcome.
This also serves as a safeguard. The nanamachines are scary. They'll do very unsightly things if left unchecked. Accordingly, they are programmed to only act like they are alive if they can detect the will of a human guiding them. The easiest way to give them that signal is to give one fluid motion that lets them see your entire body is integrated.
The result would also create a line of martial arts masters who allow this communication to work both ways. While the normal wielder simply tells the sword what to do, these masters also listen to the feedback from the nanomachines, and are willing to adjust their own positioning or stance to better suit the nanomachines. This allows the masters to unlock their full potential. While anyone can make a sword do what they want over time, a master can make the sword do what they want almost instantly, because they are so integrated that the sword knows it's still connected to a masterful human. It doens't have to worry about mixed signals.