Will it still need some sort of 4G/Wifi connection?
Yes. Online card transactions need a data connection. This is no different than a payment terminal, which in this day and age has to be connected to the internet.
Any mention by Apple of using this for IAP purchases ?
In theory, it completely eliminates the need for Apple's "curated" iOS App Store

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This is not remotely the same as IAP. This is completely in person payments, ie in a store.
Making pick pocket thieves lives easier. Good for you, Apple.
No longer will they need to risk getting caught by attempting to pick pocket someone on the subway. Now, they just have to hold their iPhone next to someone's butt wallet in their back pocket to initiate a contactless payment with their credit/debit card.
To do a transaction you need a merchant account. If you actually try this and set up an account and commit fraud, they can use the info they have on you to prosecute you for fraud and send you to prison. I assume to create an account you need names, addresses, IDs, etc. People figure these things out. Also, this fear was done years and years ago with contactless cards and as a result we couldn't have contactless cards for many years. Though it was worse then because the actual card number was wirelessly exposed and you didn't need to initiate a payment to get anything, the card number could be sent elsewhere to be charged (on the internet, in person, etc). It is true that a contactless card can be charged (although Apple Pay/Google Pay can't be charged like this because it requires you to initiate a payment and authenticate). If you have contactless cards and you're in close proximity, then I recommend an RFID blocking wallet, those are available everywhere. Or don't keep your contactless cards with you in the subway and just rely on Apple Pay/Google Pay/other phone systems.
I wonder how this will work with the IRS reporting rules.
This is just another option for Square or other payment processors to allow merchants to take payments, no impact on IRS rules at all.
Too bad this couldn't be extended back to the 6S and 7. They too have NFC capability already (including write abilities through apps), so I'd imagine its possible. But, I understand the business decision to cut product support at year five when this goes live later this year. Maybe this is a likely indicator iOS 16 won't be making it to those devices.
The earlier iPhones don't have the same NFC setup as the iPhones XS and later have. You can't even read NFC tags on earlier iPhones but you can on new ones.
I assume there will be some sort of auth/approval step?
No different than Square or other payment processors, they have an app to run the merchant payments through, this is a new API for processors. You type up your charge and then they pay on the phone, even with contactless cards. Literally the same as it was before but no extra hardware needed (but still needed for chip reading or swipes).
This is cool. I can charge people for my advice right there on the spot. ?
If you set up a merchant account only. You can do that today. Or you can use Apple Pay Cash. It's not for everyone to just take payments, it's an option for merchants to be able to go without needing separate hardware.
Some people don't seem to realize this isn't about transferring money from person to person, this is for merchants. If you send money from person to person it has to be from a type of cash account with a balance. If you send money with credit cards you get charged cash advance fees. You want to pay like $25 to send someone a few bucks, be my guest.