An easy test is to use a code or something that disables dash u-smashes. If the DACUS gets disabled too, it came from the DUS code and probably wasn't intentional. If it isn't...We'll be back where we started.
It's worth testing at least.
Anyways, I doubt it was intentional. I believe my logic for Wavedashing's disinclusion applys here too.
The way we should analyze it is like this:
What exactly causes DACUS?
Well it is a Dash Attack cancelled into an Up Smash.
Lets go step by step:
1. Dash Attacking: Was it meant to be like it is?
We can safely say dash attacks were meant to be in the game
2. Gaining momentum from said Dash Attack
It is clearly safe to assume that depending on the dash attack, some dash attacks were meant to give a "burst" of momentum, like Snakes (and not just use your running speeds momentum)
3. Cancelling the Dash Attack with an Up Smash
Was this meant to be like this? My guess is no. I don't think Sakurai ever wanted any attack to be cancelled into another attack. Probably because of the buffering or the IASA frames a glitch occured where certain attacks (specifically dash attacks) could be cancelled with an up smash, but I am pretty certain this was not something planned by Sakurai to happen.
4. Performing an Up Smash
Pretty safe to say this was intended
5. Retaining momentum from the dash attack
This probably was not meant to happen either, but this one there is no way to prove. We could argue wether momentum was supposed to be retained or not, but it is good to note that the only attack action (aside from specific specials) which retains momentum are Up-Smashes, which is kind of weird that only these attacks share this property. F-Smashing causes Stutter Step instead of retaining the momentum, tilting causes your character to stop dead on its tracks. Also momentum is reset upon landing and jumping. I would bet, even though I have no proof, that the fact that Up-Smash retains momentum is an oversight of the programming of the game and not of the design. Probably design-wise Sakurai didn't want any action to retain a previous action's momentum
Because of this I say that DACUS is most probably a glitch, although someone could probably debate otherwise, but I would like to actually hear an argument against it being a glitch.
For comparisons sake, let's do wavedashing
1. Air Dodging
Was it meant to work like this? It is is safe to assume it was
2. Gaining a burst of momentum
Was air dodge supposed to give you a burst of momentum in a certain direction? Yes, it was described as such in the very definition of the ability.
3. Retaining momentum upon landing
Retaining momentum when jump/landing was completely and purposely programmed into the game physics. Otherwise it wouldn't happen. (It's not something that just happens). Was it meant to be like this? We can say that if momentum was not desired to be retained then they would have easily noticed it on the very first play test. It is quite easy to note how you keep your running speed upon jumping and how you start running as soon as you hit the ground (if you were moving fast enough) and thus would have probably been taken out.
4. Sliding forward due to momentum and friction
We already covered that momentum had to be purposely programmed, otherwise it wouldn't happened or would have been stripped from the game. Every character has a different friction/traction ratio, so that was specifically programmed for every single character, obviously meant to be in the game.
5. Being in idle position while sliding
The burst of momentum is created from the air dodge, which was given no lag after landing, thus this make your character stand in idle animation after falling from an air dodge. Completely meant to be.
The only point that can be debated from wavedashing is point 3 and debating that specific point wouldn't be debating wavedashing, it would be debating the complete Melee Physics Engine, saying that Melee's physics as a whole were not meant to be. As such it is completely safe to assume that Wavedashing is not in fact a glitch and it is a consequence of the physics engine.