I'm a bit late to this particular party, but as someone who doesn't buy Pro iPhones the introduction of yet another tier of iPhone makes me wonder how attractive Apple will be able to keep the regular line up.
The base iPhone used to be the one that got all the new stuff, while Apple kept an older model around to sell at a cheaper price. Then they added the SE, which was basically the same phone in a different form factor. They slowly started to fragment the Pro and temporarily give it exclusive features that would eventually trickle down to the base iPhone. The iPhone 14 introduced even more fragmentation by reusing last year's chip, which means the base is a sort of halfway house that's almost an iPhone 13.
If you add in an Ultra, depending on how Apple plays it, this could mean that the base iPhone is even more behind the curve than it already is in some respects. On the one hand, Apple could truly set it apart and create a new product category that's differentiated by features that you'd never expect to come to the base models and thus wouldn't constrain them -- that could be a pen like on the Samsung Ultras or it could be a foldable. But that would fragment iOS in a way that no previous model has done and I'm not sure Apple is willing to go down that way.
So, on the other hand, their general approach would suggest that the Ultra could be yet another piece of the ladder that's supposed to upsell you while providing the exact same iPhone experience as every other model. That's great for shareholders, I guess, but for us regular iPhone users it probably means that we have to wait even longer for certain improvements. This might work out for Apple and push people to "really stretch," as Tim Cooks expects, or it might push people elsewhere unless the competition equally pushes prices endlessly.