Insufficient testing is such a crappy argument, yeah let's assume they are utterly broken and unusable. That's the starting point of the naysayers, who fail to grasp that no amount of testing will ever compare to what we will get from actually having them on. If it turns out they are actually broken, then just ****ing ban them, no loss.
Could this is be a short-sighted issue? Let's step back a bit in time instead:
Having Items on with the first Brawl tourney at Evo hurt the image so badly because the Melee scene (and other fighters) were grinning the whole time - "Not Competitive" became the stepping stone to Brawl's image.
Smash Wii U is in a similar situation where people are just waiting to kill it for not being "competitive" and Evo is the perfect chance again. I don't want to be the doomspeaker, but this is just a plain recipe being repeated and I don't want the same results.
Chances are we don't have a disaster like Items were certain to cause, but the probability is still very much a reality and holding off just one year would solve the problem. Let vanilla have it's time and make change from there with whatever toppings you'd like, but jumping straight into this is not the wisest option.
**** will never be ready. But if custom moves being on becomes the norm people will adjust in a month. There is no reason not to have customs on.
If it's not ready in a year then I would seriously doubt the competitive value of Customs.
Just making a statement saying "there is no reason not to have customs on" is not going to cut it for me, sorry.
A major rules change needs reason for the change, not shifting the burden of proof on others to need reason not to do this.
If customs are allowed, and there is either a gamebreaking bug or something is overpowered, it can be banned. Problem solved, with little to no repercussions.
This is what is called "rose tinted glasses" - Absolutely only good things will come of this. Nothing bad.
Well, no, because gamebreaking bugs and janky gameplay and exploits that people will abuse could lead many people to see Smash Wii U as that and only that. Most people will be exposed to SSBU the first time at Evo and first impressions are the strongest. Potentially bad things become compounded and lasting; I just have to point to Brawl's stigma after its first Evo appearance.
So now you might get an image of how this could actually be very bad for everyone overall and start to understand why holding off for just a year is when everyone can get behind customs happily.
Because of this, a greater divide happens between people who believe customs are "right" vs those who believe customs are "wrong". And this divide could potentially lead to customs never being allowed, due to misinformation. Because people are easily mislead by the opinions of others, especially when time is a large factor.
So everyone quit talking in terms of "us" vs "them" and start talking about what works for everyone.
The way that talk goes is someone is going to be upset when the real possibility of everyone being ok with the progress happens.
Jumping into a pool of cold water is easier than trying to ease your way in, because you will keep retracting your foot out of reflex due to your body not being adjusted to the temperature. If that is the case, I say that the best solution is to just jump right on in, because the water is fine.
Hypothermia
Your analogy is more akin to a local where not much comes out of problems, but the reality is Evo would be more like a sinking ship. Hypothermia for the entire Smash Community is like having the S.S. Titanic, which coincidentally they said was perfectly fine "unsinkable" and that no harm would come about not having proper amount of lifeboats.
I'm not getting aboard the Custom movement and will hope all who do don't meet up with an iceberg like the Titanic did.
I don't see why they don't have enough skills to not be able to react/adapt to custom moves in the same manner, as well. They will be fine.
If you're so confident maybe you'd like to pay their entrance fee.