Nope. A few inaccuracies in your post. On multiple occasions new hardware has launched with previous software. This same debate happened with iPhone X. Everyone said 11.1. It came with 11.0.3.
iOS 11.3 is not at GM stage. The iPad is coming Friday. At earliest we will see 11.3 is Monday because macOS got a new beta this week. 11 years of Apple history will outline that when one software gets a beta in a week, none get a public release in the same week.
You can think what you want. You have the right. I won’t take that from you. But just know what you are claiming has holes and assumptions.
As i said there is no trend now with apple, it just does whenever and what ever it wants to. So its always about the higher odds of something happening. Since a new major update was released along side a new product(iPad 6 in this case), the odds of them releasing on the update is higher and thats what happened.
So by that logic, then wouldn't people have found reference to the new iPad in iOS 11.3 beta?
No because if that logic were true, then people would find reference to new devices in the first beta of the new iOS version. i.e reference of iPhone 8 and iPhone X in iOS 11 Beta 1. Apple adds those details only in the GM version. and thats what i meant.