No, they would be stupid not to add 3D Touch to the iPad Air 3, because that's what it needs to run universal iPhone and iPad apps. Apple Pencil is a pro-accessory which needs pro-hardware and pro-software to be any useful. It's not an iToy for people who are bored with their iPad Airs.
I wonder will Apple upgrade the RAM on the iPad Air 3 to 4 GB. If they do, I'm retiring my iPad Air and replacing it with this.
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Yes, but that's not how the world works according to Apple. It's beneficial to manufacturing to offer as few variants as possible and it's beneficial to marketing to diversify over those few variants as much as possible and also offer different price points to get the most money out of each customer. That's why size, power and price are always linked in Apples go-to-market strategy. Everyone would want Pencil support at no additional costs, but only professionals and rich people will pay up the price to actually get it. The iPad mini is the poor mans iPad, because there must be at least one more affordable variant to serve the price-sensitive market. This model will get the new chip one year later and some features will never propagate down to the smallest, cheapest, slowest iPad. The big exception of that rule was 2013, when Apple wanted to make the 64-bit transition as quickly as possible and both iPad Air 1 and iPad mini 2 both got the same A7 chip at the same time.
If iPad Pro is too big and too expensive than you don't care enough about Apple Pencil.
If the Pencil is proving to be really popular I could see Apple bringing it to the Air line. I'm not so certain about the keyboard though. My guess is the Pro will always be differentiated with an X variant of the A chip and more RAM. And it might get new features first. I think 3D Touch will be completely dependent on whether they're able to get it working properly on larger displays.
Apple only ever reports sales numbers for iPads as a whole. Everything else you've read was an educated guess by someone who believes to be an analyst. And all this guessing is informed by personal preference, ownership of device and what was new at that time. Because there is no current 4-inch iPhone and iPhone Plus is not a total flop, some people believe phablets will eat small tablets market share entirely. But a new smaller, cheaper iPhone could outsell the plus-size as soon as next quarter and provoke new predictions. We'll never know. You better only ask yourself what size fits me?
It's always tough to convince people they need a second iOS device. All iPhone owners big or small, have less reason to also buy an iPad. But that's also true the other way around, iPad owners have less reason to buy a big, expensive iPhone Plus or an even more expensive MacBook. (Assuming Android and Windows are perceived as cheap trash not worth owning at all.) iPads with more memory and faster processors are the most powerful iOS devices with a higher longevity than iPhones and they are cheaper too. Unless you actually have to call people, I don't know why to own an iPhone?
A more hybrid iOS/OSX OS would also help sales.
