Domain names translate semantic meaning into internet addresses. They're for people. They're designed to be read and understood by people. If they're hard to understand, they're not doing what they're intended to do.
Like many people, I had mixed feelings about the new generic top-level domain (gTLD) offering. While some domains like .guru or .club seemed like a good way to get pressure off of the toxic .com market, there are many bizarre new gTLDs like .whoswho. But on the whole, I was mildly in favor of the new gTLDs despite persuasive arguments from the Coalition for Responsible Internet Domain Oversight.
That is, until I found out that many come in pairs. I recently saw the gTLD .pet in a list, and I thought it was odd choice. Who would make a domain for one single pet1? But ICANN thought of this and added .pets.
So now we have two gTLDs: .pet and .pets. I am absolutely sure, that if there's a popular pet website I want to go to in the future, I won't be able to remember if they pluralized their gTLD or not. And this goes against what domain names were meant to do: translate meaning. If I can't remember it, then it's not doing the right thing.
To those who say search engines have obviated the need for remembering domain names, that is only partially true. Physical and television advertisements have URLs in them. Phishing uses the fact that people don't understand domains to extract money from them. People email URLs all the time.
If you are part a company or group that in any way needs to protect your users – really, any website where you can log in, you should not use one of the new pluralizable gTLDs. They will confuse your users and you will be worse off. Here's a list of gTLDs that users may mistake for one another2:
.car/.cars .deal/.deals .fan/.fans .home/.homes .hotel/.hotels .loan/.loans .market/.marketing/.markets .mov/.movie .new/.news .pet/.pets .photo/.photos .property/.properties .realestate/.realtor/.reatly .review/.reviews .supply/.supplies .tour/.tours .work/.works
You owe it to your users to be as easy-to-use as possible. That means not making them remember whether or not your gTLD is plural or if which noun form it is. This means you'll have to buy more than one, and redirect, which just creates more work and more expense.
Stick to a simple domain for now, and avoid these plural gTLDs.
Update: I was informed that the owners of .sport successfully objected to the .sports domain. So ICANN, in principle, agrees. Read the objection to .sports for yourself.